Advance in microRNA as a potential biomarker for early detection of pancreatic cancer.

Pancreatic cancer is characterized as a disease with low survival and high mortality because of no effective diagnostic and therapeutic strategies available in clinic. Conventional clinical diagnostic methods including serum markers and radiological imaging (CT, MRI, EUS, etc.) often fail to detect precancerous or early stage lesions. Development of effective biomarkers is unmet for reduction of mortality of pancreatic cancer. MicroRNAs (miRNAs) are a group of small non-protein-coding RNAs playing roles in regulation of cell physiology including tumorigenesis, apoptotic escape, proliferation, invasion, epithelial-mesenchymal transition (EMT), metastasis and chemoresistance. Various altered signaling pathways involving in molecular pathogenesis of pancreatic cancer are mediated by miRNAs as a role of either oncogenes or tumor suppressors. Among biomarkers developed including protein, metabolites, DNA, RNA, epigenetic mutation, miRNAs are superior because of its unique chemical property. Recent study suggests that miRNAs may be promising biomarkers used for early detection of pancreatic cancer. This review will update the progression made in early detection of pancreatic cancer.

Inhibition of Pyruvate Dehydrogenase Kinase 2 Protects Against Hepatic Steatosis Through Modulation of Tricarboxylic Acid Cycle Anaplerosis and Ketogenesis.

Hepatic steatosis is associated with increased insulin resistance and tricarboxylic acid (TCA) cycle flux, but decreased ketogenesis and pyruvate dehydrogenase complex (PDC) flux. This study examined whether hepatic PDC activation by inhibition of pyruvate dehydrogenase kinase 2 (PDK2) ameliorates these metabolic abnormalities. Wild-type mice fed a high-fat diet exhibited hepatic steatosis, insulin resistance, and increased levels of pyruvate, TCA cycle intermediates, and malonyl-CoA but reduced ketogenesis and PDC activity due to PDK2 induction. Hepatic PDC activation by PDK2 inhibition attenuated hepatic steatosis, improved hepatic insulin sensitivity, reduced hepatic glucose production, increased capacity for ß-oxidation and ketogenesis, and decreased the capacity for lipogenesis. These results were attributed to altered enzymatic capacities and a reduction in TCA anaplerosis that limited the availability of oxaloacetate for the TCA cycle, which promoted ketogenesis. The current study reports that increasing hepatic PDC activity by inhibition of PDK2 ameliorates hepatic steatosis and insulin sensitivity by regulating TCA cycle anaplerosis and ketogenesis. The findings suggest PDK2 is a potential therapeutic target for nonalcoholic fatty liver disease.

The Warburg effect: a balance of flux analysis.

Cancer metabolism is characterized by increased macromolecular syntheses through coordinated increases in energy and substrate metabolism. The observation that cancer cells produce lactate in an environment of oxygen sufficiency (aerobic glycolysis) is a central theme of cancer metabolism known as the Warburg effect. Aerobic glycolysis in cancer metabolism is accompanied by increased pentose cycle and anaplerotic activities producing energy and substrates for macromolecular synthesis. How these processes are coordinated is poorly understood. Recent advances have focused on molecular regulation of cancer metabolism by oncogenes and tumor suppressor genes which regulate numerous enzymatic steps of central glucose metabolism. In the past decade, new insights in cancer metabolism have emerged through the application of stable isotopes particularly from 13C carbon tracing. Such studies have provided new evidence for system-wide changes in cancer metabolism in response to chemotherapy. Interestingly, experiments using metabolic inhibitors on individual biochemical pathways all demonstrate similar system-wide effects on cancer metabolism as in targeted therapies. Since biochemical reactions in the Warburg effect place competing demands on available precursors, high energy phosphates and reducing equivalents, the cancer metabolic system must fulfill the condition of balance of flux (homeostasis). In this review, the functions of the pentose cycle and of the tricarboxylic acid (TCA) cycle in cancer metabolism are analyzed from the balance of flux point of view. Anticancer treatments that target molecular signaling pathways or inhibit metabolism alter the invasive or proliferative behavior of the cancer cells by their effects on the balance of flux (homeostasis) of the cancer metabolic phenotype.

NOTCH reprograms mitochondrial metabolism for proinflammatory macrophage activation.

Metabolic reprogramming is implicated in macrophage activation, but the underlying mechanisms are poorly understood. Here, we demonstrate that the NOTCH1 pathway dictates activation of M1 phenotypes in isolated mouse hepatic macrophages (HMacs) and in a murine macrophage cell line by coupling transcriptional upregulation of M1 genes with metabolic upregulation of mitochondrial oxidative phosphorylation and ROS (mtROS) to augment induction of M1 genes. Enhanced mitochondrial glucose oxidation was achieved by increased recruitment of the NOTCH1 intracellular domain (NICD1) to nuclear and mitochondrial genes that encode respiratory chain components and by NOTCH-dependent induction of pyruvate dehydrogenase phosphatase 1 (Pdp1) expression, pyruvate dehydrogenase activity, and glucose flux to the TCA cycle. As such, inhibition of the NOTCH pathway or Pdp1 knockdown abrogated glucose oxidation, mtROS, and M1 gene expression. Conditional NOTCH1 deficiency in the myeloid lineage attenuated HMac M1 activation and inflammation in a murine model of alcoholic steatohepatitis and markedly reduced lethality following endotoxin-mediated fulminant hepatitis in mice. In vivo monocyte tracking further demonstrated the requirement of NOTCH1 for the migration of blood monocytes into the liver and subsequent M1 differentiation. Together, these results reveal that NOTCH1 promotes reprogramming of mitochondrial metabolism for M1 macrophage activation.

High oleic/stearic fatty-acid desaturation index in cord plasma from infants of mothers with gestational diabetes.

OBJECTIVE: Enhanced fatty-acid desaturation by stearoyl-CoA desaturase enzyme-1 (SCD1) is associated with obesity. This study determined desaturation in the cord plasma of newborns of mothers with and without gestational diabetes (GDM). STUDY DESIGN: Newborns of mothers with GDM (n=21) and without (control, n=22) were recruited. Cord plasma fatty-acid desaturation indices (palmitoleic/palmitic, oleic/stearic ratios) were compared, and correlated with anthropometrics and biochemical measures. A subset of very low-density lipoprotein (VLDL) desaturation indices were determined to approximate the liver SCD1 activity. RESULT: The total oleic/stearic index was higher in GDM, despite adjustment for cord glucose concentrations. Among GDM and controls, the oleic/stearic index correlated with cord glucose concentrations (rs=0.36, P=0.02). Both palmitoleic/palmitic and oleic/stearic indices correlated with waist circumference (r=0.47, P=0.001; r=0.37, P=0.01). The VLDL oleic/stearic index was higher in GDM. CONCLUSION: The elevated total oleic/stearic index suggests increased lipogenesis in GDM newborns. Factors in addition to glucose supply may influence fetal SCD1 activity.

Testosterone replacement ameliorates nonalcoholic fatty liver disease in castrated male rats.

Nonalcoholic fatty liver disease is common in developed countries and is associated with obesity, metabolic syndrome, and type 2 diabetes. T deficiency is a risk factor for developing these metabolic deficiencies, but its role in hepatic steatosis has not been well studied. We investigated the effects of T on the pathogenesis of hepatic steatosis in rats fed a high-fat diet (HFD). Adult male rats were randomly placed into four groups and treated for 15 weeks: intact rats on regular chow diet (RCD), intact rats on liquid HFD (I+HFD), castrated rats on HFD (C+HFD), and castrated rats with T replacement on HFD (C+HFD+T). Fat contributed 71% energy to the HFD but only 16% of energy to the RCD. Serum T level was undetectable in castrated rats, and T replacement led to 2-fold higher mean serum T levels than in intact rats. C+HFD rats gained less weight but had higher percentage body fat than C+HFD+T. Severe micro- and macrovesicular fat accumulated in hepatocytes with multiple inflammatory foci in the livers of C+HFD. I+HFD and C+HFD+T hepatocytes demonstrated only mild to moderate microvesicular steatosis. T replacement attenuated HFD-induced hepatocyte apoptosis in castrated rats. Serum glucose and insulin levels were not increased with HFD in any group. Immunoblots showed that insulin-regulated proteins were not changed in any group. This study demonstrates that T deficiency may contribute to the severity of hepatic steatosis and T may play a protective role in hepatic steatosis and nonalcoholic fatty liver disease development without insulin resistance.

Glucose intolerance and lipid metabolic adaptations in response to intrauterine and postnatal calorie restriction in male adult rats.

Enhanced de novo lipogenesis (DNL), an adult hepatic adaption, is seen with high carbohydrate or low-fat diets. We hypothesized that ad libitum intake after prenatal calorie restriction will result in adult-onset glucose intolerance and enhanced DNL with modified lipid metabolic gene expression profile. Stable isotopes were used in 15-month-old adult male rat offspring exposed to prenatal (IUGR), pre- and postnatal (IPGR), or postnatal (PNGR) caloric restriction vs. controls (CON). IUGR vs. CON were heavier with hepatomegaly but unchanged visceral white adipose tissue (WAT), glucose intolerant with reduced glucose-stimulated insulin secretion (GSIS), pancreatic ß-cell mass, and total glucose clearance rate but unsuppressed hepatic glucose production. Liver glucose transporter (Glut) 1 and DNL increased with decreased hepatic acetyl-CoA carboxylase (ACC) and fatty acid synthase but increased WAT fatty acid transport protein-1 and peroxisomal proliferator-activated receptor-γ, resistin, and visfatin gene expression. In contrast, PNGR and IPGR were lighter, had reduced visceral WAT, and were glucose tolerant with unchanged hepatic glucose production but with increased GSIS, ß-cell mass, glucose clearance rate, and WAT insulin receptor. Hepatic Glut1 and DNL were also increased in lean IPGR and PNGR with increased hepatic ACC, phosphorylated ACC, and pAMPK and reduced WAT fatty acid transport protein-1, peroxisomal proliferator-activated receptor-γ, and ACCα. We conclude the following: 1) the heavy, glucose-intolerant and insulin-resistant IUGR adult phenotype is ameliorated by postnatal caloric restriction; 2) increased DNL paralleling hepatic Glut1 is a biomarker of exposure to early caloric restriction rather than the adult metabolic status; 3) hepatic lipid enzyme expression reflects GSIS rather than DNL; and 4) WAT gene expression reflects an obesogenic vs. lean phenotype.

Prenatal rosiglitazone administration to neonatal rat pups does not alter the adult metabolic phenotype.

Prenatally administered rosiglitazone (RGZ) is effective in enhancing lung maturity; however, its long-term safety remains unknown. This study aimed to determine the effects of prenatally administered RGZ on the metabolic phenotype of adult rats. Methods. Pregnant Sprague-Dawley rat dams were administered either placebo or RGZ at embryonic days 18 and 19. Between 12 and 20 weeks of age, the rats underwent glucose and insulin tolerance tests and de novo fatty acid synthesis assays. The lungs, liver, skeletal muscle, and fat tissue were processed by Western hybridization for peroxisome proliferator-activated receptor (PPAR)γ, adipose differentiation-related protein (ADRP), and surfactant proteins B (SPB) and C (SPC). Plasma was assayed for triglycerides, cholesterol, insulin, glucagon, and troponin-I levels. Lungs were also morphometrically analyzed. Results. Insulin and glucose challenges, de novo fatty acid synthesis, and all serum assays revealed no differences among all groups. Western hybridization for PPARγ, ADRP, SPB, and SPC in lung, liver, muscle, and fat tissue showed equal levels. Histologic analyses showed a similar number of alveoli and septal thickness in all experimental groups. Conclusions. When administered prenatally, RGZ does not affect long-term fetal programming and may be safe for enhancing fetal lung maturation.

Hyperinsulinism presenting in childhood and treatment by conservative pancreatectomy.

OBJECTIVE: To describe the uncommon presentation of hyperinsulinism in an 8-year-old boy. METHODS: We describe the patient's clinical findings, results from biochemical and imaging studies, surgical approach, and outcome. The discussion encompasses a review of literature that provided the basis for the diagnostic and surgical approach applied to this patient's case. RESULTS: An obese 8.5-year-old boy initially presented with hypoglycemic seizures after initiation of dietary changes to treat obesity. Biochemical analysis indicated hyperinsulinism. Endoscopic ultrasonography showed no pancreatic lesions suggestive of insulinoma. Genetic studies identified no known mutations in the ABCC8, KCNJ11, GCK, or GLUD1 genes. Selective arterial calcium stimulation and hepatic venous sampling did not document a focal source for hyperinsulinism in the pancreas, and positron emission tomography with 18-fluoro-L-3,4-dihydroxyphenylalanine showed diffusely increased uptake in the pancreas. The patient ultimately required partial pancreatectomy because of continued hypoglycemia while taking diazoxide and octreotide. Intraoperative glucose monitoring directed the extent of surgical resection. A 45% pancreatectomy was performed, which resolved the hypoglycemia but led to impaired glucose tolerance after surgery. CONCLUSION: The unusual presentation of hyperinsulinism in childhood required a personalized approach to diagnosis and surgical management using intraoperative glucose monitoring that resulted in a conservative pancreatectomy.

Fasting induces ketoacidosis and hypothermia in PDHK2/PDHK4-double-knockout mice.

The importance of PDHK (pyruvate dehydrogenase kinase) 2 and 4 in regulation of the PDH complex (pyruvate dehydrogenase complex) was assessed in single- and double-knockout mice. PDHK2 deficiency caused higher PDH complex activity and lower blood glucose levels in the fed, but not the fasted, state. PDHK4 deficiency caused similar effects, but only after fasting. Double deficiency intensified these effects in both the fed and fasted states. PDHK2 deficiency had no effect on glucose tolerance, PDHK4 deficiency produced only a modest effect, but double deficiency caused a marked improvement and also induced lower insulin levels and increased insulin sensitivity. In spite of these beneficial effects, the double-knockout mice were more sensitive than wild-type and single-knockout mice to long-term fasting, succumbing to hypoglycaemia, ketoacidosis and hypothermia. Stable isotope flux analysis indicated that hypoglycaemia was due to a reduced rate of gluconeogenesis and that slightly more glucose was converted into ketone bodies in the double-knockout mice. The findings establish that PDHK2 is more important in the fed state, PDHK4 is more important in the fasted state, and survival during long-term fasting depends upon regulation of the PDH complex by both PDHK2 and PDHK4.

Postnatal rosiglitazone administration to neonatal rat pups does not alter the young adult metabolic phenotype.

BACKGROUND: Rosiglitazone (RGZ), a peroxisome proliferator-activated receptor-γ (PPARγ) agonist, significantly enhances lung maturation without affecting blood biochemical and metabolic profiles in the newborn period. However, whether this exposure to RGZ in neonatal life alters the adult metabolic phenotype is not known. OBJECTIVE: To determine the effects of early postnatal administration of RGZ on the young adult metabolic phenotype. METHODS: Newborn rat pups were administered either saline or RGZ for the first 7 days of life. At 11-14 weeks, glucose and insulin tolerance tests and deuterium labeling were performed. Blood and tissues were analyzed for various metabolic parameters. RESULTS: Overall, there was no effect of early postnatal RGZ administration on young adult body weight, glucose and insulin tolerance, plasma cholesterol and triglyceride profiles, insulin, glucagon, cardiac troponin, fatty acid synthesis, or tissue adipogenic differentiation. CONCLUSIONS: Treatment with RGZ in early neonatal life does not alter later developmental metabolic programming or lead to an altered metabolic phenotype in the young adult, further re-enforcing the safety of PPARγ agonists as a novel lung-protective strategy.

Turnover of nonessential fatty acids in cardiolipin from the rat heart.

Cardiolipin (CL) is a unique phospholipid (PL) found in the mitochondria of mammalian cells. CL remodeling is accompanied by turnover of its fatty acid acyl groups. Abnormalities in CL remodeling have been found in Barth's syndrome, diabetes, and obesity. The objective of this study was to determine nonessential fatty acid turnover in CL and phosphatidylethanolamine (PE) in the rat heart in vivo. Sprague-Dawley rats were fed either a regular chow or a high-fat diet for 15 weeks, and consumed 6% deuterium-enriched drinking water as a tracer for 14 days. CL and PE were extracted from cardiac tissue and isolated by TLC. Fatty acids from CL, PE, and plasma were analyzed by GC/MS for deuterium incorporation. Results showed oleate and vaccenate turnover were the highest in CL whereas palmitate and stearate turnover were low. Among the nonessential fatty acids in PE, turnover of stearate and vaccenate were the highest. The high turnover rate in vaccenate was unexpected, because vaccenate previously had no known metabolic or physiologic function. In conclusion, the similarly high turnover rates of both oleate and vaccenate readily suggest that remodeling is an important functional aspect of PL metabolism in CL.

Tracer-based metabolomics: concepts and practices.

Tracer-based metabolomics is a systems biology tool that combines advances in tracer methodology for physiological studies, high throughput "-omics" technologies and constraint based modeling of metabolic networks. It is different from the commonly known metabolomics or metabonomics in that it is a targeted approach based on a metabolic network model in cells. Because of its complexity, it is the least understood among the various "-omics." In this review, the development of concepts and practices of tracer-based metabolomics is traced from the early application of radioactive isotopes in metabolic studies to the recent application of stable isotopes and isotopomer analysis using mass spectrometry; and from the modeling of biochemical reactions using flux analysis to the recent theoretical formulation of the constraint based modeling. How these newer experimental methods and concepts of constraint-based modeling approaches can be applied to metabolic studies is illustrated by examples of studies in determining metabolic responses of cells to pharmacological agents and nutrient environment changes.

Advantages of dynamic "closed loop" stable isotope flux phenotyping over static "open loop" clamps in detecting silent genetic and dietary phenotypes.

In vivo insulin sensitivity can be assessed using "open loop" clamp or "closed loop" methods. Open loop clamp methods are static, and fix plasma glucose independently from plasma insulin. Closed loop methods are dynamic, and assess glucose disposal in response to a stable isotope labeled glucose tolerance test. Using PPARalpha(-/-) mice, open and closed loop assessments of insulin sensitivity/glucose disposal were compared. Indirect calorimetry done for the assessment of diurnal substrate utilization/metabolic flexibility showed that chow fed PPARalpha(-/-) mice had increased glucose utilization during the light (starved) cycle. Euglycemic clamps showed no differences in insulin stimulated glucose disposal, whether for chow or high fat diets, but did show differences in basal glucose clearance for chow fed PPARalpha(-/-) versus SV129J-wt mice. In contrast, the dynamic stable isotope labeled glucose tolerance tests reveal enhanced glucose disposal for PPARalpha(-/-) versus SV129J-wt, for chow and high fat diets. Area under the curve for plasma labeled and unlabeled glucose for PPARalpha(-/-) was approximately 1.7-fold lower, P < 0.01 during the stable isotope labeled glucose tolerance test for both diets. Area under the curve for plasma insulin was 5-fold less for the chow fed SV129J-wt (P < 0.01) but showed no difference on a high fat diet (0.30 +/- 0.1 for SV129J-wt vs. 0.13 +/- 0.10 for PPARalpha(-/-), P = 0.28). This study demonstrates that dynamic stable isotope labeled glucose tolerance test can assess "silent" metabolic phenotypes, not detectable by the static, "open loop", euglycemic or hyperglycemic clamps. Both open loop and closed loop methods may describe different aspects of metabolic inflexibility and insulin sensitivity.

Measurement of glucose and fructose in clinical samples using gas chromatography/mass spectrometry.

OBJECTIVE: The impact of increased fructose consumption on carbohydrate metabolism is a topic of current interest, but determination of serum level has been hindered due to low concentration and interference from serum glucose. We are reporting a method for the quantification of glucose and fructose in clinical samples using gas chromatography/mass spectrometry (GC/MS). The accuracy and precision of GC/MS and an enzymatic assay were compared. DESIGN AND METHODS: Mass spectrometry fragmentation patterns of methyloxime peracetate derivatized aldose and ketose were determined. Unique fragments for glucose and fructose were used for quantitative analysis using isotope labeled recovery standards. RESULTS: Methyloxime peracetate derivatives of glucose and fructose showed characteristic loss of acetate (M-60) or ketene (M-42) under chemical ionization (CI). Under electron impact (EI) ionization, a unique C1-C2 fragment of glucose was formed, while a C1-C3 fragment was formed from keto-hexoses. These unique fragments were used in the quantitative assay of glucose and fructose in clinical samples. In clinical samples, the GC/MS assay has a lower limit of detection than that of the enzymatic assay. In plasma samples from patients evaluated for diabetes the average serum glucose and fructose were 6.19+/-2.72 mM and 46+/- 25.22 microM. Fructose concentrations in many of these samples were below the limit of detection of the enzymatic method. CONCLUSION: Derivatization of aldose and ketose monosaccharides to their respective O-methyloxime acetates for GC/MS analysis is a facile method for determination of serum/plasma glucose and fructose samples.

A novel, view-independent method for strain mapping in myocardial elastography: eliminating angle and centroid dependence.

Robust indices of regional and global cardiac function are a key factor in detection and treatment of heart disease as well as understanding of the fundamental mechanisms of a healthy heart. Myocardial elastography provides a noninvasive method for imaging and measuring displacement and strain of the myocardium for the early detection of cardiovascular disease. However, two-dimensional in-plane axial and lateral strains measured depend on the sonographic view used. This becomes especially critical in a clinical setting and may induce large variations in the measured strains, potentially leading to false diagnoses. A novel method in myocardial elastography is proposed for eliminating this view dependence by deriving the polar, principal and classified principal strains. The performance of the proposed methodology is assessed by employing 3D finite-element left-ventricular models of a control and an ischemic canine heart. Although polar strains are angle-independent, they are sensitive to the selected reference coordinate system, which requires the definition of a centroid of the left ventricle (LV). In contrast, principal strains derived through eigenvalue decomposition exhibit the inherent characteristic of coordinate system independence, offering view (i.e., angle and centroid)-independent strain measurements. Classified principal strains are obtained by assigning the principal components in the physical ventricular coordinate system. An extensive strain analysis illustrates the improvement in interpretation and visualization of the full-field myocardial deformation by using the classified principal strains, clearly depicting the ischemic and non-ischemic regions. Strain maps, independent of sonographic views and imaging planes, that can be used to accurately detect regional contractile dysfunction are demonstrated.

Systems analysis of energy metabolism elucidates the affected respiratory chain complex in Leigh's syndrome.

Leigh's syndrome is a complex neurological disease with little known correlation between causes and symptoms. Mutations in pyruvate dehydrogenase and electron transport chain complexes have been associated with this syndrome, although the identification of affected enzymes is difficult, if not impossible, with non-invasive clinical tests. In this study, isotopomer analysis is used to characterize the metabolic phenotype of normal and Leigh's syndrome fibroblasts (GM01503), thereby identifying affected enzymes in the diseased cells. Fibroblasts are grown with DMEM media enriched with (13)C labeled glucose. Amino acids from media and proteins as well as lactate are analyzed with GC-MS to identify their label distributions. A computational model accounting for all major pathways in fibroblast metabolism (including 430 metabolites and 508 reactions) is built to determine the metabolic steady states of the normal and Leigh's cell lines based on measured substrate uptake and secretion rates and isotopomer data. Results show that (i) Leigh's syndrome affected cells have slower metabolism than control fibroblasts as evidenced by their overall slower substrate utilization and lower secretion of end products; (ii) intracellular fluxes predicted by the models, some of which are validated by biochemical studies published in the literature, show that the respiratory chain in Leigh's affected cells can produce ATP at a similar rate as the controls, but with a more restricted flux range; and (iii) mutations causing the defects observed in the Leigh's cells are likely to be in succinate cytochrome c reductase.

Increased pentose phosphate pathway flux after clinical traumatic brain injury: a [1,2-13C2]glucose labeling study in humans.

Patients with traumatic brain injury (TBI) routinely exhibit cerebral glucose uptake in excess of that expected by the low levels of oxygen consumption and lactate production. This brings into question the metabolic fate of glucose. Prior studies have shown increased flux through the pentose phosphate cycle (PPC) during cellular stress. This study assessed the PPC after TBI in humans. [1,2-(13)C(2)]glucose was infused for 60 mins in six consented, severe-TBI patients (GCS<9) and six control subjects. Arterial and jugular bulb blood sampled during infusion was analyzed for (13)C-labeled isotopomers of lactate by gas chromatography/mass spectroscopy. The product of lactate concentration and fractional abundance of isotopomers was used to determine blood concentration of each isotopomer. The difference of jugular and arterial concentrations determined cerebral contribution. The formula PPC=(m1/m2)/(3+(m1/m2)) was used to calculate PPC flux relative to glycolysis. There was enrichment of [1,2-(13)C(2)]glucose in arterial-venous blood (enrichment averaged 16.6% in TBI subjects and 28.2% in controls) and incorporation of (13)C-label into lactate, showing metabolism of labeled substrate. The PPC was increased in TBI patients relative to controls (19.6 versus 6.9%, respectively; P=0.002) and was excellent for distinguishing the groups (AUC=0.944, P<0.0001). No correlations were found between PPC and other clinical parameters, although PPC was highest in patients studied within 48 h of injury (averaging 33% versus 13% in others; P=0.0006). This elevation in the PPC in the acute period after severe TBI likely represents a shunting of substrate into alternative biochemical pathways that may be critical for preventing secondary injury and initiating recovery.

Decreased hepatic futile cycling compensates for increased glucose disposal in the Pten heterodeficient mouse.

Despite altered regulation of insulin signaling, Pten(+/-) heterodeficient standard diet-fed mice, approximately 4 months old, exhibit normal fasting glucose and insulin levels. We report here a stable isotope flux phenotyping study of this "silent" phenotype, in which tissue-specific insulin effects in whole-body Pten(+/-)-deficient mice were dissected in vivo. Flux phenotyping showed gain of function in Pten(+/-) mice, seen as increased peripheral glucose disposal, and compensation by a metabolic feedback mechanism that 1) decreases hepatic glucose recycling via suppression of glucokinase expression in the basal state to preserve hepatic glucose production and 2) increases hepatic responsiveness in the fasted-to-fed transition. In Pten(+/-) mice, hepatic gene expression of glucokinase was 10-fold less than wild-type (Pten(+/+)) mice in the fasted state and reached Pten(+/+) values in the fed state. Glucose-6-phosphatase expression was the same for Pten(+/-) and Pten(+/+) mice in the fasted state, and its expression for Pten(+/-) was 25% of Pten(+/+) in the fed state. This study demonstrates how intra- and interorgan flux compensations can preserve glucose homeostasis (despite a specific gene defect that accelerates glucose disposal) and how flux phenotyping can dissect these tissue-specific flux compensations in mice presenting with a "silent" phenotype.