Synthesis, transfer, and phosphorylation of phosphoinositides in cardiac membranes

Oxidation of hyperpolarized [1-13 C]pyruvate in isolated rat kidneys

Kidneys play a central role in numerous disorders but current imaging methods have limited utility to probe renal metabolism. Hyperpolarized (HP) 13 C magnetic resonance imaging is uniquely suited to provide metabolite-specific information about key biochemical pathways and it offers the further advantage that renal imaging is practical in humans. This study evaluated the feasibility of hyperpolarization examinations in a widely used model for analysis of renal physiology, the isolated kidney, which enables isolation of renal metabolism from the effects of other organs and validation of HP results by independent measurements. Isolated rat kidneys were supplied with either HP [1-13 C]pyruvate only or HP [1-13 C]pyruvate plus octanoate. Metabolic activity in both groups was confirmed by stable renal oxygen consumption. HP [1-13 C]pyruvate was readily metabolized to [13 C]bicarbonate, [1-13 C]lactate, and [1-13 C]alanine, detectable seconds after HP [1-13 C]pyruvate was injected. Octanoate suppressed but did not eliminate the production of HP [13 C]bicarbonate from [1-13 C]pyruvate. Steady-state flux analyses using non-HP 13 C substrates validated the utilization of HP [1-13 C]pyruvate, as observed by HP 13 C NMR. In the presence of octanoate, lactate is generated from a tricarboxylic acid cycle intermediate, oxaloacetate. The isolated rat kidney may serve as an excellent model for investigating and establishing new HP 13 C metabolic probes for future kidney imaging applications.

Branched-chain α-ketoacids are preferentially reaminated and activate protein synthesis in the heart

Branched-chain amino acids (BCAA) and their cognate α-ketoacids (BCKA) are elevated in an array of cardiometabolic diseases. Here we demonstrate that the major metabolic fate of uniformly-¹³C-labeled α-ketoisovalerate ([U-¹³C]KIV) in the heart is reamination to valine. Activation of cardiac branched-chain α-ketoacid dehydrogenase (BCKDH) by treatment with the BCKDH kinase inhibitor, BT2, does not impede the strong flux of [U-¹³C]KIV to valine. Sequestration of BCAA and BCKA away from mitochondrial oxidation is likely due to low levels of expression of the mitochondrial BCAA transporter SLC25A44 in the heart, as its overexpression significantly lowers accumulation of [¹³C]-labeled valine from [U-¹³C]KIV. Finally, exposure of perfused hearts to levels of BCKA found in obese rats increases phosphorylation of the translational repressor 4E-BP1 as well as multiple proteins in the MEK-ERK pathway, leading to a doubling of total protein synthesis. These data suggest that elevated BCKA levels found in obesity may contribute to pathologic cardiac hypertrophy via chronic activation of protein synthesis.

Systemic modulation of branched-chain keto acid (BCKA) metabolism alters cardiac health. Here, the authors define the major fates of BCKA in the heart and demonstrate that acute exposure to BCKA levels found in obesity activates cardiac protein synthesis and markedly alters the heart phosphoproteome.

Isoliquiritigenin Attenuates UUO-Induced Renal Inflammation and Fibrosis by Inhibiting Mincle/Syk/NF-Kappa B Signaling Pathway

Purpose

Chronic kidney disease (CKD) is a global nephrotic syndrome characterized by chronic inflammation, oxidative stress and fibrosis in the kidney. Isoliquiritigenin (ISL), a flavonoid from licorice, has historically been reported to inhibit innate immune responses to inflammation and fibrosis in vivo. However, the effect of ISL on CKD progression is largely unknown.

Materials and Methods

In this study, we employed the inflammatory and fibrotic models of LPS/TGF-β-induced bone marrow-derived macrophages (BMDM) in vitro and unilateral ureteral obstruction (UUO) model in vivo to explore the potential effects and mechanism of ISL on renal inflammation and fibrosis.

Results

Our results manifest that ISL improved UUO-induced renal dysfunction and reduced tubular damage with a significantly downregulated mRNA expression and secretion of IL-1β, IL-6, TNF-α and MCP-1 in vitro and in vivo. It is worth noting that ISL can strongly inhibit the mRNA and protein expression of Mincle (macrophage-induced c-type lectin) in BMDM and UUO. ISL inhibited the phosphorylation of Syk and NF-kappa B and simultaneously reduced the expression of α-SMA and Col III in vivo and in vitro. More interestingly, when dealing with TDB, a ligand of Mincle, it revealed significant reversal of protein expression levels as that observed with ISL. The expressions of IL-1β, IL-6, TNF-α, iNOS, p-Syk, p-NF-kappa B, α-SMA and FN in BMDM inflammatory model were significantly upregulated with TDB treatment. This confirms that ISL inhibits inflammation and fibrosis of macrophage by suppressing Mincle/Syk/NF-kappa B signaling pathway.

Conclusion

To conclude, ISL protects UUO-induced CKD by inhibiting Mincle-induced inflammation and suppressing renal fibrosis, which might be a specific renal protective mechanism of ISL, making it a novel drug to ameliorate CKD.

Cost-effectiveness of angiotensin-converting enzyme inhibitors versus angiotensin II receptor blockers as first-line treatment in autosomal dominant polycystic kidney disease

BACKGROUND

Autosomal dominant polycystic kidney disease (ADPKD) is a rare kidney disorder impacting ∼1:2,500 individuals among the general US population. Hypertension is a significant predictor of ADPKD progression, and a risk factor for development of cardiovascular disease (CVD), the most common cause for mortality among ADPKD patients. Angiotensin-converting enzymes inhibitors (ACE-I) are widely used as first-line treatment in ADPKD for the management of hypertension. However, their cost-effectiveness relative to other hypertensive medications, such as angiotensin II receptor blockers (ARB), has never been assessed.

OBJECTIVE

To determine if ARB are more cost-effective than ACE-Is as first-line treatment in ADPKD.

METHODS

A Markov-state decision model was constructed for estimation of cost and outcome benefits in hypertensive ADPKD patients. Transition probabilities were extrapolated from a retrospective cohort study comparing chronic kidney disease (CKD) stage transitions in ADPKD patients. Annual pharmaceutical costs per average daily dose per CKD stage were extracted from a US healthcare claims database. Median total healthcare costs per CKD stage or transplant were extracted from the published literature. The time horizon was set to 30 years, with 1-year duration to cycle shift. A cost-effectiveness analysis was conducted to estimate the incremental cost-effectiveness ratio (ICER) of ACE-I vs ARB per additional year of prevented transplant and/or death. A one-way probabilistic sensitivity analysis was conducted, with 10% variation in probabilities and cost.

RESULTS

Total annual healthcare costs accrued after 30 years among ADPKD patients taking ACE-Is was estimated to be $3,505,028.41, compared to ARB at $3,644,327.65. Life expectancy was increased by 1.39 years among patients taking ACE-I. Approximate 10-year survival in patients taking ACE-Is was 47% compared to ARB at 34%.

CONCLUSIONS

ACE-I dominated ARB and displayed greater cost-effectiveness due to lower cost and increased capacity to prolong years of life without transplant or death among hypertensive ADPKD patients. This model strengthens the value of ACE-I over ARB as first-line treatment for hypertension management in ADPKD patients.

High-Throughput Indirect Quantitation of 13C Enriched Metabolites Using 1H NMR

Nuclear magnetic resonance (NMR) spectroscopy is widely used in metabolomics to perform quantitative profiling of low-molecular weight compounds from biological specimens. The measurement of endogenous metabolites using NMR has proven to be a powerful tool to identify new metabolic biomarkers in physiological and pathological conditions, and to study and evaluate treatment efficiency. In this study we present a rapid approach to indirectly quantify ¹³C enriched molecules using one-dimensional (1D) ¹H NMR. We demonstrate this approach using isotopically labeled [1,6-¹³C]glucose and in four different cell lines. We confirm the applicability of this approach for treatment follow-up, utilizing a renal cancer cell line with rapamycin as a tool compound to study changes in metabolic profiles. Finally, we validate the applicability of this method to study metabolic biomarkers from ex vivo tumor extracts, after infusion, using isotopically enriched glucose. Given the high throughput and increased sensitivity of direct-detect ¹H NMR, this analytical approach provides an avenue for simple and rapid metabolic analysis of biological samples including blood, urine, and biopsies.

Measuring changes in substrate utilization in the myocardium in response to fasting using hyperpolarized [1-(13)C]butyrate and [1-(13)C]pyruvate

Cardiac dysfunction is often associated with a shift in substrate preference for ATP production. Hyperpolarized (HP) ¹³C magnetic resonance spectroscopy (MRS) has the unique ability to detect real-time metabolic changes in vivo due to its high sensitivity and specificity. Here a protocol using HP [1-¹³C]pyruvate and [1-¹³C]butyrate is used to measure carbohydrate versus fatty acid metabolism in vivo. Metabolic changes in fed and fasted Sprague Dawley rats (n = 36) were studied at 9.4 T after tail vein injections. Pyruvate and butyrate competed for acetyl-CoA production, as evidenced by significant changes in [¹³C]bicarbonate (−48%), [1-¹³C]acetylcarnitine (+113%), and [5-¹³C]glutamate (−63%), following fasting. Butyrate uptake was unaffected by fasting, as indicated by [1-¹³C]butyrylcarnitine. Mitochondrial pseudoketogenesis facilitated the labeling of the ketone bodies [1-¹³C]acetoacetate and [1-¹³C]β-hydroxybutyryate, without evidence of true ketogenesis. HP [1-¹³C]acetoacetate was increased in fasting (250%) but decreased during pyruvate co-injection (−82%). Combining HP ¹³C technology and co-administration of separate imaging agents enables noninvasive and simultaneous monitoring of both fatty acid and carbohydrate oxidation. This protocol illustrates a novel method for assessing metabolic flux through different enzymatic pathways simultaneously and enables mechanistic studies of the changing myocardial energetics often associated with disease.

Production of hyperpolarized 13CO2 from [1-13C]pyruvate in perfused liver does reflect total anaplerosis but is not a reliable biomarker of glucose production

In liver, 13CO2 can be generated from [1-13C] pyruvate via pyruvate dehydrogenase or anaplerotic entry of pyruvate into the TCA cycle followed by decarboxylation at phosphoenolpyruvate carboxykinase (PEPCK), the malic enzyme, isocitrate dehydrogenase, or α-ketoglutarate dehydrogenase. The purpose of this study was to determine the relative importance of these pathways in production of hyperpolarized (HP) 13CO2 after administration of hyper-polarized pyruvate in livers supplied with a fatty acid plus substrates for gluconeogenesis. Isolated mouse livers were perfused with a mixture of thermally-polarized 13C-enriched pyruvate, lactate and octanoate in various combinations prior to exposure to HP pyruvate. Under all perfusion conditions, HP malate, aspartate and fumarate were detected within ~ 3 s showing that HP [1-13C]pyruvate is rapidly converted to [1-13C]oxaloacetate which can subsequently produce HP 13CO2 via decarboxylation at PEPCK. Measurements using HP [2-13C]pyruvate allowed the exclusion of reactions related to TCA cycle turnover as sources of HP 13CO2. Direct measures of O2 consumption, ketone production, and glucose production by the intact liver combined with 13C isotopomer analyses of tissue extracts yielded a comprehensive profile of metabolic flux in perfused liver. Together, these data show that, even though the majority of HP 13CO2 derived from HP [1-13C]pyruvate in livers exposed to fatty acids reflects decarboxylation of [4-13C]oxaloacetate (PEPCK) or [4-13C]malate (malic enzyme), the intensity of the HP 13CO2 signal is not proportional to glucose production because the amount of pyruvate returned to the TCA cycle via PEPCK and pyruvate kinase is variable, depending upon available substrates.

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.

Quantification of high-resolution ¹H-[¹³C] NMR spectra from rat brain extracts

NMR spectroscopy in combination with (13)C-labeled substrate infusion is a unique technique to obtain information about dynamic metabolic fluxes noninvasively in vivo. In many cases, the in vivo information content obtained during dynamic (13)C studies in rodents can be enhanced by high-resolution (1)H-[(13)C] NMR spectroscopy on brain extracts. Previously, it has been shown that (1)H NMR spectra from rat brain extracts can be accurately quantified with a spectral fitting routine utilizing simulated basis sets using complete prior knowledge of chemical shifts and scalar couplings. The introduction of (13)C label into the various metabolites presents complications that demand modifications of the spectral fitting routine. As different multiplets within a given molecule accumulate various amounts of (13)C label, the fixed amplitude relationship between multiplets typical for (1)H NMR spectra must be abandoned. In addition, (13)C isotope effects lead to spectral multiplet patterns that become dependent on the amount of (13)C label accumulation, thereby preventing the use of a common basis set. Here a modified spectral fitting routine is presented that accommodates variable (13)C label accumulation and (13)C isotope effects. Spectral fitting results are quantitatively compared to manual integration on column-separated samples in which spectral overlap is minimized.

Hypertension and left ventricular hypertrophy in autosomal dominant polycystic kidney disease

Hypertension is a common problem in patients with autosomal dominant polycystic kidney disease affecting both renal and patient survival. Activation of the renin-angiotensin-aldosterone system due to cyst expansion and local renal ischemia has been proposed to play an important role in the development of hypertension in autosomal dominant polycystic kidney disease. Left ventricular hypertrophy, a major cardiovascular risk factor, is also common in patients with autosomal dominant polycystic kidney disease. Both hypertension and the activation of the renin-angiotensin-aldosterone system play a role in the development of left ventricular hypertrophy in these patients. Prospective randomized results indicate that aggressive control of blood pressure is important for the optimal reversal of left ventricular hypertrophy, thereby diminishing a major risk factor for cardiovascular morbidity and mortality of patients with autosomal dominant polycystic kidney disease. There is also substantial epidemiological support for aggressive control of blood pressure in slowing renal disease progression in autosomal dominant polycystic kidney disease patients. Blockade of the renin-angiotensin-aldosterone system should be the initial approach in the treatment of hypertension in these patients.

(1)H NMR based metabolic profiling of day 2 spent embryo media correlates with implantation potential

Morphological assessment is currently the primary technique for selection of viable embryos for uterine transfer during assisted reproductive techniques, however this method has limited predictive power. The objective of this study was to employ NMR based metabolic profiling analysis of spent embryo culture media to identify novel biomarkers of embryo viability and provide insight into the metabolism of a viable embryo. A total of 37 patients undergoing IVF/ICSI treatment were recruited and 58 media samples were collected from embryos that were transferred back to the uterus. 1H NMR spectra were acquired and analyzed resulting in the quantification of 12 metabolites in the media samples. Analysis of metabolite ratios revealed significant differences between those patients with positive (n = 27) and negative (n = 31) urinary βhCG results. Some of the most biologically relevant differences include a 17% increase in the formate to glycine ratio and a 22% decrease in the citrate to alanine ratio in the spent embryo media from the positive pregnancy group. Overall, the results indicate that metabolic profiling may provide a means of identifying biomarkers that aid selection of viable embryos.

Flux through hepatic pyruvate carboxylase and phosphoenolpyruvate carboxykinase detected by hyperpolarized 13C magnetic resonance

In the heart, detection of hyperpolarized [(13)C]bicarbonate and (13)CO(2) by magnetic resonance (MR) after administration of hyperpolarized [1-(13)C]pyruvate is caused exclusively by oxidative decarboxylation of pyruvate via the pyruvate dehydrogenase complex (PDH). However, liver mitochondria possess alternative anabolic pathways accessible by [1-(13)C]pyruvate, which may allow a wider diagnostic range for hyperpolarized MR compared with other tissue. Metabolism of hyperpolarized [1-(13)C]pyruvate in the tricarboxylic acid (TCA) cycle was monitored in the isolated perfused liver from fed and fasted mice. Hyperpolarized [1-(13)C]pyruvate was rapidly converted to [1-(13)C]lactate, [1-(13)C]alanine, [1-(13)C]malate, [4-(13)C]malate, [1-(13)C]aspartate, [4-(13)C]aspartate, and [(13)C]bicarbonate. Livers from fasted animals had increased lactate:alanine, consistent with elevated NADH:NAD(+). The appearance of asymmetrically enriched malate and aspartate indicated high rates of anaplerotic pyruvate carboxylase activity and incomplete equilibration with fumarate. Hyperpolarized [(13)C]bicarbonate was also detected, consistent with multiple mechanisms, including cataplerotic decarboxylation of [4-(13)C]oxaloacetate via phosphoenolpyruvate carboxykinase (PEPCK), forward TCA cycle flux of [4-(13)C]oxaloacetate to generate (13)CO(2) at isocitrate dehydrogenase, or decarboxylation of [1-(13)C]pyruvate by PDH. Isotopomer analysis of liver glutamate confirmed that anaplerosis was sevenfold greater than flux through PDH. In addition, signal from [4-(13)C]malate and [4-(13)C]aspartate was markedly blunted and signal from [(13)C]bicarbonate was completely abolished in livers from PEPCK KO mice, indicating that the major pathway for entry of hyperpolarized [1-(13)C]pyruvate into the hepatic TCA cycle is via pyruvate carboxylase, and that cataplerotic flux through PEPCK is the primary source of [(13)C]bicarbonate. We conclude that MR detection of hyperpolarized TCA intermediates and bicarbonate is diagnostic of pyruvate carboxylase and PEPCK flux in the liver.

Inhibition of inflammation by pentosan polysulfate impedes the development and progression of severe diabetic nephropathy in aging C57B6 mice

Inflammation has a key role in diabetic nephropathy (DN) progression. Pentosan polysulfate (PPS) has been shown to decreases interstitial inflammation and glomerulosclerosis in 5/6 nephrectomized rats. Since PPS has an excellent long-term safety profile in interstitial cystitis treatment, and we recently found that old diabetic C57B6 mice develop DN characterized by extensive tubulointerstitial inflammatory lesions that mimics human DN, we examined the effect of PPS on old diabetic mice. We also examined the anti-inflammatory properties of PPS in renal cells in vitro. Diabetes was induced with streptozotocin in 18 months female (early aging) C57B6 mice. Mice were then randomized to receive oral PPS (25 mg/kg/day) or water for 4 months. The effect of PPS on NF-κB activation and on TNFα, high glucose or advanced glycation end products (AGEs) stimulated proinflammatory gene expression in renal cells was examined. We found that PPS treatment preserved renal function, significantly reduced albuminuria, and markedly decreased the severity of renal lesions, including tubulointerstitial inflammation. PPS also reduced upregulation of TNFα and proinflammatory genes in aging diabetic kidneys. Furthermore, PPS suppressed NF-κB, decreased the proinflammatory actions of TNFα, and decreased high glucose and AGEs stimulated MCP-1 production in vitro. Finally, PPS decreased TNFα-induced increase in albumin permeability in podocyte monolayers. In conclusion, PPS treatment largely prevents the development/progression of nephropathy in aging diabetic mice. As this may be mediated by suppression of TNFα, high glucose, and AGE-stimulated NF-κB activation and inflammation in vitro, the in vivo blockade of DN may be due to the anti-inflammatory properties of PPS.

Imaging myocardial metabolic remodeling

Myocardial metabolic remodeling is the process in which the heart loses its ability to utilize different substrates, becoming dependent primarily on the metabolism of a single substrate such as glucose or fatty acids for energy production. Myocardial metabolic remodeling is central to the pathogenesis of a variety of cardiac disease processes such as left ventricular hypertrophy, myocardial ischemia, and diabetic cardiomyopathy. As a consequence, there is a growing demand for accurate noninvasive imaging approaches of various aspects of myocardial substrate metabolism that can be performed in both humans and small-animal models of disease, facilitating the crosstalk between the bedside and the bench and leading to improved patient management paradigms. SPECT, PET, and MR spectroscopy are the most commonly used imaging techniques. Discussed in this review are the strengths and weaknesses of these various imaging methods and how they are furthering our understanding of the role of myocardial remodeling in cardiovascular disease. In addition, the role of ultrasound to detect the inflammatory response to myocardial ischemia will be discussed.

Modeling isotopomer distributions in biochemical networks using isotopomer mapping matrices

Within the last decades NMR spectroscopy has undergone tremendous development and has become a powerful analytical tool for the investigation of intracellular flux distributions in biochemical networks using (13)C-labeled substrates. Not only are the experiments much easier to conduct than experiments employing radioactive tracer elements, but NMR spectroscopy also provides additional information on the labeling pattern of the metabolites. Whereas the maximum amount of information obtainable with (14)C-labeled substrates is the fractional enrichment in the individual carbon atom positions, NMR spectroscopy can also provide information on the degree of labeling at neighboring carbon atom positions by analyzing multiplet patterns in NMR spectra or using 2-dimensional NMR spectra. It is possible to quantify the mole fractions of molecules that show a specific labeling pattern, i.e., information of the isotopomer distribution in metabolite pools can be obtained. The isotopomer distribution is the maximum amount of information that in theory can be obtained from (13)C-tracer studies. The wealth of information contained in NMR spectra frequently leads to overdetermined algebraic systems. Consequently, fluxes must be estimated by nonlinear least squares analysis, in which experimental labeling data is compared with simulated steady state isotopomer distributions. Hence, mathematical models are required to compute the steady state isotopomer distribution as a function of a given set of steady state fluxes. Because 2(n) possible labeling patterns exist in a molecule of n carbon atoms, and each pattern corresponds to a separate state in the isotopomer model, these models are inherently complex. Model complexity, so far, has restricted usage of isotopomer information to relatively small metabolic networks. A general methodology for the formulation of isotopomer models is described. The model complexity of isotopomer models is reduced to that of classical metabolic models by expressing the 2(n) isotopomer mass balances of a metabolite pool in a single matrix equation. Using this approach an isotopomer model has been implemented that describes label distribution in primary carbon metabolism, i.e., in a metabolic network including the Embden-Meyerhof-Parnas and pentose phosphate pathway, the tricarboxylic acid cycle, and selected anaplerotic reaction sequences. The model calculates the steady state label distribution in all metabolite pools as a function of the steady state fluxes and is applied to demonstrate the effect of selected anaplerotic fluxes on the labeling pattern of the pathway intermediates.

Tissue-specific short chain fatty acid metabolism and slow metabolic recovery after ischemia from hyperpolarized NMR in vivo

Mechanistic details of mammalian metabolism in vivo and dynamic metabolic changes in intact organisms are difficult to monitor because of the lack of spatial, chemical, or temporal resolution when applying traditional analytical tools. These limitations can be addressed by sensitivity enhancement technology for fast in vivo NMR assays of enzymatic fluxes in tissues of interest. We apply this methodology to characterize organ-specific short chain fatty acid metabolism and the changes of carnitine and coenzyme A pools in ischemia reperfusion. This is achieved by assaying acetyl-CoA synthetase and acetyl-carnitine transferase catalyzed transformations in vivo. The fast and predominant flux of acetate and propionate signal into acyl-carnitine pools shows the efficient buffering of free CoA levels. Sizeable acetyl-carnitine formation from exogenous acetate is even found in liver, where acetyl-CoA synthetase and acetyl-carnitine transferase activities have been assumed sequestered in different compartments. In vivo assays of altered acetate metabolism were applied to characterize pathological changes of acetate metabolism upon ischemia. Coenzyme pools in ischemic skeletal muscle are reduced in vivo even 1 h after disturbing muscle perfusion. Impaired mitochondrial metabolism and slow restoration of free CoA are corroborated by assays employing fumarate to show persistently reduced tricarboxylic acid (TCA) cycle activity upon ischemia. In the same animal model, anaerobic metabolism of pyruvate and tissue perfusion normalize faster than mitochondrial bioenergetics.

Increased glucose uptake and oxidation in mouse hearts prevent high fatty acid oxidation but cause cardiac dysfunction in diet-induced obesity

BACKGROUND

Shift of myocardial substrate preference has been observed in many chronic diseases such as diabetes and heart failure. This study was undertaken to elucidate the mechanisms underlying the chronic substrate switch in adult hearts and to determine the functional consequences of the switch.

METHODS AND RESULTS

Transgenic mice with cardiac-specific overexpression of the insulin-independent glucose transporter GLUT1 (TG) were used to increase intracellular glucose in cardiac myocytes. A high-fat diet was used to increase the fatty acid supply to the heart. High-fat diet induced a 40% increase in fatty acid oxidation in wild-type hearts, whereas glucose oxidation was decreased to 30% of the control. In contrast, glucose oxidation was >2-fold higher in TG hearts, and the high-fat diet failed to upregulate fatty acid oxidation in these hearts. Glucose induced changes in the expression of multiple metabolic genes, including peroxisome proliferator-activated receptor-alpha (decreased by 51%), 3-oxoacid CoA transferase (decreased by 67%), and acetyl-CoA carboxylase (increased by 4-fold), resulting in a remodeling of the metabolic network to favor a shift of substrate preference toward glucose. Although TG mice on a normal diet maintained normal cardiac energetics and function, the inability to upregulate myocardial fatty acid oxidation in TG mice fed a high-fat diet resulted in increased oxidative stress in the heart, activation of p38 mitogen-activated protein kinase, and contractile dysfunction.

CONCLUSIONS

We have demonstrated that chronic increases in myocardial glucose uptake and oxidation reduce the metabolic flexibility and render the heart susceptible to contractile dysfunction.

c-Myc activates multiple metabolic networks to generate substrates for cell-cycle entry

Cell proliferation requires the coordinated activity of cytosolic and mitochondrial metabolic pathways to provide ATP and building blocks for DNA, RNA and protein synthesis. Many metabolic pathway genes are targets of the c-myc oncogene and cell-cycle regulator. However, the contribution of c-Myc to the activation of cytosolic and mitochondrial metabolic networks during cell-cycle entry is unknown. Here, we report the metabolic fates of [U-(13)C] glucose in serum-stimulated myc(-/-) and myc(+/+) fibroblasts by (13)C isotopomer NMR analysis. We demonstrate that endogenous c-myc increased (13)C labeling of ribose sugars, purines and amino acids, indicating partitioning of glucose carbons into C1/folate and pentose phosphate pathways, and increased tricarboxylic acid cycle turnover at the expense of anaplerotic flux. Myc expression also increased global O-linked N-acetylglucosamine protein modification, and inhibition of hexosamine biosynthesis selectively reduced growth of Myc-expressing cells, suggesting its importance in Myc-induced proliferation. These data reveal a central organizing function for the Myc oncogene in the metabolism of cycling cells. The pervasive deregulation of this oncogene in human cancers may be explained by its function in directing metabolic networks required for cell proliferation.

Mitochondrial dysfunction contributes to impaired insulin secretion in INS-1 cells with dominant-negative mutations of HNF-1alpha and in HNF-1alpha-deficient islets

Maturity Onset Diabetes of the Young-type 3 (MODY-3) has been linked to mutations in the transcription factor hepatic nuclear factor (HNF)-1alpha, resulting in deficiency in glucose-stimulated insulin secretion. In INS-1 cells overexpressing doxycycline-inducible HNF-1alpha dominant-negative (DN-) gene mutations, and islets from Hnf-1alpha knock-out mice, insulin secretion was impaired in response to glucose (15 mm) and other nutrient secretagogues. Decreased rates of insulin secretion in response to glutamine plus leucine and to methyl pyruvate, but not potassium depolarization, indicate defects specific to mitochondrial metabolism. To identify the biochemical mechanisms responsible for impaired insulin secretion, we used (31)P NMR measured mitochondrial ATP synthesis (distinct from glycolytic ATP synthesis) together with oxygen consumption measurements to determine the efficiency of mitochondrial oxidative phosphorylation. Mitochondrial uncoupling was significantly higher in DN-HNF-1alpha cells, such that rates of ATP synthesis were decreased by approximately one-half in response to the secretagogues glucose, glutamine plus leucine, or pyruvate. In addition to closure of the ATP-sensitive K(+) channels with mitochondrial ATP synthesis, mitochondrial production of second messengers through increased anaplerotic flux has been shown to be critical for coupling metabolism to insulin secretion. (13)C-Isotopomer analysis and tandem mass spectrometry measurement of Krebs cycle intermediates revealed a negative impact of DN-HNF-1alpha and Hnf-1alpha knock-out on mitochondrial second messenger production with glucose but not amino acids. Taken together, these results indicate that, in addition to reduced glycolytic flux, uncoupling of mitochondrial oxidative phosphorylation contributes to impaired nutrient-stimulated insulin secretion with either mutations or loss of HNF-1alpha.

Intermittent Pressure-Loading Increases Transforming Growth Factor-Beta-1 Secretion from Renal Tubular Epithelial Cells: In vitro Vesicoureteral Reflux Model

BACKGROUND

To investigate the effect of hydrodynamic pressure mimicking vesicoureteral reflux on renal tubular epithelial cells in vitro, we constructed an intermittent pressure-loading (IPL) model of Madin-Darby canine kidney (MDCK) cells.

MATERIALS AND METHODS

Three grades of pressure were loaded onto the MDCK cells intermittently. The concentration of cytokines in the supernatant, the amount of the protein and its mRNA in the MDCK cells were studied, respectively.

RESULTS

After 24 h, the concentration of transforming growth factor-beta1 (TGF-beta1) increased under intense IPL conditions (100 and 200 cm H2O) in the 15-min IPL group (p<0.05, p<0.01). The amount of cellular level of TGF-beta1 protein and its mRNA did not show any significant increase within 24 h under the present conditions. The concentration of monocyte chemoattractant peptide-1 (MCP-1) was not significantly different from that of the control.

CONCLUSION

These data suggest that the early TGF-beta1 secretion phenomenon without change in gene expression is the case in the renal tubular epithelial cells under certain intermittent pressure-loading conditions.

Compensated cardiac hypertrophy is characterised by a decline in palmitate oxidation

Cardiac hypertrophy is an independent risk factor in the development of heart failure. However, the cellular mechanisms underlying the transition from compensated hypertrophy to heart failure are incompletely understood. The aim of this study was to investigate changes in myocardial substrate utilisation and function in pressure-overload hypertrophy (using 13C NMR spectroscopy) in parallel with alterations in the expression pattern of genes involved in cardiac fatty acid and glucose uptake and oxidation. Left ventricular hypertrophy was induced surgically in Sprague-Dawley rats by inter-renal aortic constriction. Nine weeks later, hearts were perfused in the isovolumic mode with a physiological mixture of substrates including 5 mM 1-13C glucose, 1 mM 3-13C lactate, 0.1 mM U-13C pyruvate and 0.3 mM U-13C palmitate and cardiac function monitored simultaneously. Real-time PCR was used to determine mRNA levels of PPARalpha and PPARalpha-regulated metabolic enzymes. Results showed that at the stage of compensated hypertrophy, fatty acid oxidation (FAO) and expression of genes involved in FAO were markedly reduced, whilst pyruvate oxidation was enhanced, highlighting the fact that metabolic remodelling is an early event in the development of cardiac hypertrophy.

Visual exploration of isotope labeling networks in 3D

Isotope labeling networks (ILNs) are graphs explaining the flow of isotope labeled molecules in a metabolic network. Moreover, they are the structural backbone of metabolic flux analysis (MFA) by isotopic tracers which has been established as a standard experimental tool in fluxomics. To configure an isotope labeling experiment (ILE) for MFA, the structure of the corresponding ILN must be understood to a certain extent even by a practitioner. Graph algorithms help to analyze the network structure but produce rather abstract results. Here, the major obstruction is the high dimension of these networks and the large number of network components which, consequently, are hard to figure out manually. At the interface between theory and experiment, the three-dimensional interactive visualization tool CumoVis has been developed for exploring the network structure in a step by step manner. Navigation and orientation within ILNs are supported by exploiting the natural 3D structure of an underlying metabolite network with stacked labeled particles on top of each metabolite node. Network exploration is facilitated by rotating, zooming, forward and backward path tracing and, most important, network component reduction. All features of CumoVis are explained with an educational example and a realistic network describing carbon flow in the citric acid cycle.

Hyperpolarized 13C allows a direct measure of flux through a single enzyme-catalyzed step by NMR

(13)C NMR is a powerful tool for monitoring metabolic fluxes in vivo. The recent availability of automated dynamic nuclear polarization equipment for hyperpolarizing (13)C nuclei now offers the potential to measure metabolic fluxes through select enzyme-catalyzed steps with substantially improved sensitivity. Here, we investigated the metabolism of hyperpolarized [1-(13)C(1)]pyruvate in a widely used model for physiology and pharmacology, the perfused rat heart. Dissolved (13)CO(2), the immediate product of the first step of the reaction catalyzed by pyruvate dehydrogenase, was observed with a temporal resolution of approximately 1 s along with H(13)CO(3)(-), the hydrated form of (13)CO(2) generated catalytically by carbonic anhydrase. In hearts presented with the medium-chain fatty acid octanoate in addition to hyperpolarized [1-(13)C(1)]pyruvate, production of (13)CO(2) and H(13)CO(3)(-) was suppressed by approximately 90%, whereas the signal from [1-(13)C(1)]lactate was enhanced. In separate experiments, it was shown that O(2) consumption and tricarboxylic acid (TCA) cycle flux were unchanged in the presence of added octanoate. Thus, the rate of appearance of (13)CO(2) and H(13)CO(3)(-) from [1-(13)C(1)]pyruvate does not reflect production of CO(2) in the TCA cycle but rather reflects flux through pyruvate dehydrogenase exclusively.

Carbohydrate-response element-binding protein deletion alters substrate utilization producing an energy-deficient liver

Livers from mice lacking the carbohydrate-responsive element-binding protein (ChREBP) were compared with wild type (WT) mice to determine the effect of this transcription factor on hepatic energy metabolism. The pyruvate dehydrogenase complex was considerably more active in ChREBP(-/-) mice because of diminished pyruvate dehydrogenase kinase activity. Greater pyruvate dehydrogenase complex activity caused a stimulation of lactate and pyruvate oxidation, and it significantly impaired fatty acid oxidation in perfused livers from ChREBP(-/-) mice. This shift in mitochondrial substrate utilization led to a 3-fold reduction of the free cytosolic [NAD(+)]/[NADH] ratio, a 1.7-fold increase in the free mitochondrial [NAD(+)]/[NADH] ratio, and a 2-fold decrease in the free cytosolic [ATP]/[ADP][P(i)] ratio in the ChREBP(-/-) liver compared with control. Hepatic pyruvate carboxylase flux was impaired with ChREBP deletion secondary to decreased fatty acid oxidation, increased pyruvate oxidation, and limited pyruvate availability because of reduced activity of liver pyruvate kinase and malic enzyme, which replenish pyruvate via glycolysis and pyruvate cycling. Overall, the shift from fat utilization to pyruvate and lactate utilization resulted in a decrease in the energy of ATP hydrolysis and a hypo-energetic state in the livers of ChREBP(-/-) mice.

Regulation of c-fos, c-jun and c-myc Gene Expression by Angiotensin II in Primary Cultured Rat Astrocytes: Role of ERK1/2 MAP Kinases

We have previously shown that angiotensin II (Ang II) stimulates astrocyte growth through activation of ERK1/2 mitogen activated protein (MAP) kinases. In the current study, we determined whether Ang II stimulates the expression of c-fos, c-jun and c-myc in brainstem astrocyte cultures. Reverse transcriptase-PCR analysis showed c-fos, c-jun, and c-myc mRNAs were induced by Ang II. The EC50 values for Ang II stimulation of c-fos, c-jun and c-myc were 1.3, 1.68 and 1.4 nM, respectively. Ang II (100 nM) induced peak stimulation for all genes by 45 min followed by a gradual decline. Inhibition of ERK1/2 by PD98059 attenuated Ang II-induced c-fos and c-myc mRNA expression (by 75% and 100%, respectively) but was ineffective in preventing Ang II induction of c-jun. These studies show for the first time in brainstem astrocytes that Ang II induces the expression of c-fos, c-myc and c-jun, and showed that ERK1/2 mediate Ang II stimulation of c-fos and c-myc. These data implicate the ERK1/2 MAP kinase pathway as a divergent point in controlling Ang II stimulation of immediate early response genes in the central nervous system.

Long-term effects of increased glucose entry on mouse hearts during normal aging and ischemic stress

BACKGROUND

A shift of substrate preference toward glucose in the heart is considered a reversion to fetal metabolic profile, but its role in the pathogenesis of cardiac diseases is incompletely understood.

METHODS AND RESULTS

We performed a 2-year follow-up study in transgenic mice with sustained high glucose uptake and utilization in the heart by cardiac-specific overexpression of the insulin-independent glucose transporter GLUT1 (GLUT1-TG). Compared with wild-type litter mates, the GLUT1-TG mice showed a normal survival rate and unaltered contractile function of the heart monitored by serial echocardiography and by pressure-volume studies in isolated perfused hearts in the 2-year period. Furthermore, when hearts were subjected to ischemia-reperfusion, cardiac function of young and old GLUT1-TG recovered to the same level (86% and 83%, respectively) and exceeded that of both young and old wild-type hearts (52% and 35%, respectively; P<0.05). Nuclear magnetic resonance spectroscopic measurements with 31P showed delayed ATP depletion, reduced acidosis during ischemia, and improved recovery of high-energy phosphate content in old GLUT1-TG hearts (P<0.05 versus old wild-type). During reperfusion, glucose oxidation was 3-fold higher and fatty acid oxidation was 45% lower in old GLUT1-TG hearts compared with old wild-type (P<0.05), which suggests that the deleterious effects of excessive fatty acid oxidation during reperfusion was prevented in old GLUT1-TG hearts.

CONCLUSIONS

We have demonstrated that a normal heart is able to adapt to long-term increases in basal glucose entry into cardiomyocytes without development of glucotoxicity. Furthermore, life-long increases in glucose uptake result in a favorable metabolic phenotype that affords protections against aging-associated increase of susceptibility to ischemic injury.

Differential regulation of Toll-like receptor 4 gene expression in renal cells by angiotensin II: dependency on AP1 and PU.1 transcriptional sites

BACKGROUND

Toll-like receptor 4 (TLR4) is involved in the sensing of lipopolysaccharide and, therefore, plays a central role in innate immune responses to gram-negative bacteria. Interestingly, TLR4 expression occurs within the kidney. We have previously demonstrated that angiotensin II (ANG II) upregulates TLR4 expression on mesangial cells. However, the factors controlling transcriptional activation of the Tlr4 gene in mesangial cells are not known, and the specificity of this response for other renal cells is unclear.

METHODS

Cultured murine proximal tubular cells (mouse cortical tubule cell line; MCT cells), murine mesangial cells (MMCs), and murine podocytes were treated with ANG II. The expression of ANG II receptor mRNA and TLR4 mRNA and protein was determined by polymerase chain reaction and Western blotting. The transcriptional activity of wild-type and mutant mouse TLR4 promoter reporter constructs was determined upon transient transfection of the three cell types.

RESULTS

Although MMCs, podocytes, and syngeneic proximal MCT cells similarly expressed ANG II receptors, ANG II stimulated TLR4 mRNA and protein expression in MMCs and podocytes only. A mouse TLR4 promoter construct (-518/+129), previously shown to contain all important transcriptional regulatory elements in various cell types, was activated by ANG II in MMCs and podocytes, but not in MCT cells. Mutation of a proximal PU.1-binding consensus site or an AP1 site abolished ANG-II-mediated transcriptional activation of the TLR4 promoter. Finally, basal transcription of the Tlr4 gene depended in all three cell lines on an intact AP1 site and additionally on the proximal PU.1 site in MMCs.

CONCLUSIONS

ANG II stimulates TLR4 transcription through AP1 and PU.1 sites in a cell-specific manner. Since the intrarenal ANG II concentrations are enhanced in many pathophysiological situations, ANG-II-stimulated transcription of TLR4 on MMCs and podocytes may contribute to renal inflammation.

Prolonged exposure to homocysteine results in diminished but reversible pancreatic beta-cell responsiveness to insulinotropic agents

BACKGROUND

Plasma homocysteine levels may be elevated in poorly controlled diabetes with pre-existing vascular complications and/or nephropathy. Since homocysteine has detrimental effects on a wide diversity of cell types, the present study examined the effects of long-term homocysteine exposure on the secretory function of clonal BRIN-BD11 beta-cells.

METHODS

Acute insulin secretory function, cellular insulin content and viability of BRIN-BD11 cells were assessed following long-term (18 h) exposure to homocysteine in culture. RT-PCR and Western blot analysis were used to determine the expression of key beta-cell genes and proteins. Cells were cultured for a further 18 h without homocysteine to determine any long-lasting effects.

RESULTS

Homocysteine (250-1000 micromol/L) exposure reduced insulin secretion at both moderate (5.6 mmol/L) and stimulatory (16.7 mmol/L) glucose by 48-63%. Similarly, insulin secretory responsiveness to stimulatory concentrations of alanine, arginine, 2-ketoisocaproate, tolbutamide, KCl, elevated Ca2+, forskolin and PMA, GLP-1, GIP and CCK-8 were reduced by 11-62% following culture with 100-250 micromol/L homocysteine. These inhibitory effects could not simply be attributed to changes in cellular insulin content, cell viability, H2O2 generation or any obvious alterations of gene/protein expression for insulin, glucokinase, GLUT2, VDCC, or Kir6.2 and SUR1. Additional culture for 18 h in standard culture media after homocysteine exposure restored secretory responsiveness to all agents tested.

CONCLUSION

These findings suggest that long-term exposure to high homocysteine levels causes a reversible impairment of pancreatic beta-cell insulinotropic pathways. The in vivo actions of hyperhomocysteinaemia on islet cell function merit investigation.

Aberrant activation of AMP-activated protein kinase remodels metabolic network in favor of cardiac glycogen storage

AMP-activated protein kinase (AMPK) responds to impaired cellular energy status by stimulating substrate metabolism for ATP generation. Mutation of the gamma2 regulatory subunit of AMPK in humans renders the kinase insensitive to energy status and causes glycogen storage cardiomyopathy via unknown mechanisms. Using transgenic mice expressing one of the mutant gamma2 subunits (N488I) in the heart, we found that aberrant high activity of AMPK in the absence of energy deficit caused extensive remodeling of the substrate metabolism pathways to accommodate increases in both glucose uptake and fatty acid oxidation in the hearts of gamma2 mutant mice via distinct, yet synergistic mechanisms resulting in selective fuel storage as glycogen. Increased glucose entry in the gamma2 mutant mouse hearts was directed through the remodeled metabolic network toward glycogen synthesis and, at a substantially higher glycogen level, recycled through the glycogen pool to enter glycolysis. Thus, the metabolic consequences of chronic activation of AMPK in the absence of energy deficiency is distinct from those previously reported during stress conditions. These findings are of particular importance in considering AMPK as a target for the treatment of metabolic diseases.

Myocardial function, energy provision, and carnitine deficiency in experimental uremia

Cardiac complications are the leading cause of mortality in patients with chronic renal failure. Secondary carnitine deficiency, which is frequently observed in hemodialysis patients, has been associated with cardiac hypertrophy and heart failure and may impair myocardial fatty acid oxidation. In chronic kidney disease, impaired carnitine homeostasis also may affect myocardial metabolism. In this study, myocardial function and substrate oxidation in conjunction with carnitine deficiency were investigated in experimental renal failure. Uremia was induced in male Sprague-Dawley rats via a two-stage five-sixths nephrectomy. Cardiac function and substrate oxidation were assessed in vitro by means of isovolumic perfusion using 13C nuclear magnetic resonance at 3 and 6 wk of uremia. Renal impairment as assessed by serum creatinine was more severe initially and was associated with a significant deficiency in serum free carnitine (43%; P < 0.001) and elevated acyl carnitine/free carnitine ratio. Myocardial tissue carnitine concentrations, however, were unaffected. A moderate degree of cardiac hypertrophy (10 to 14%; P < 0.05) was observed in uremia without evidence of dysfunction or changes in myocardial substrate utilization. It is concluded that renal dysfunction is associated with cardiac hypertrophy in the presence of normal myocardial carnitine levels, despite a significant depletion in serum carnitine. This may be a factor in maintaining normal cardiac function and metabolism.

Cytosolic and mitochondrial malic enzyme isoforms differentially control insulin secretion

In islet beta-cells and INS-1 cells both the high activity of malic enzyme and the correlation of insulin secretion rates with pyruvate carboxylase (PC) flux suggest that a pyruvate-malate cycle is functionally relevant to insulin secretion. Expression of the malic enzyme isoforms in INS-1 cells and rat islets was measured, and small interfering RNA was used to selectively reduce isoform mRNA expression in INS-1 cells to evaluate its impact on insulin secretion. The cytosolic NADP(+)-specific isoform (ME1) was the most abundant, with the mitochondrial isoforms NAD(+)-preferred (ME2) expressed at approximately 50%, and the NADP(+)-specific (ME3) at approximately 10% compared with ME1. Selective reduction (89 +/- 2%) of cytosolic ME1 mRNA expression and enzyme activity significantly reduced glucose (15 mM:41 +/- 6%, p < 0.01) and amino acid (4 mM glutamine +/- 10 mM leucine: 39 +/- 6%, p < 0.01)-stimulated insulin secretion. Selective small interfering RNA reduction (51 +/- 6%) of mitochondrial ME2 mRNA expression did not impact glucose-induced insulin secretion, but decreased amino acid-stimulated insulin secretion by 25 +/- 4% (p < 0.01). Modeling of the metabolism of [U-(13)C]glucose by its isotopic distribution in glutamate indicates a second pool of pyruvate distinct from glycolytically derived pyruvate in INS-1 cells. ME1 knockdown decreased flux of both pools of pyruvate through PC. In contrast, ME2 knockdown affected only PC flux of the pyruvate derived from glutamate metabolism. These results suggest a physiological basis for two metabolically and functionally distinct pyruvate cycles. The cycling of pyruvate by ME1 generates cytosolic NADPH, whereas mitochondrial ME2 responds to elevated amino acids and serves to supply sufficient pyruvate for increased Krebs cycle flux when glucose is limiting.

Investigation of the effects of sulfonylurea exposure on pancreatic beta cell metabolism

Prolonged exposure of pancreatic beta cells to the sulfonylureas glibencamide and tolbutamide induces subsequent desensitization to the actions of these drugs. The precise mechanisms underlying this desensitization remain unknown, prompting the present study, which investigated the impact of prolonged sulfonylurea exposure on glucose and energy metabolism using clonal pancreatic BRIN-BD11 beta cells. Following prolonged exposure to tolbutamide, BRIN-BD11 beta cells were incubated in the presence of [U-(13)C]glucose, and isotopomer analysis revealed that there was a change in the ratio of flux through pyruvate carboxylase (EC 6.4.1.1) and pyruvate dehydrogenase (EC 1.2.4.1, EC 2.3.1.12, EC 1.8.1.4). Energy status in intact BRIN-BD11 cells was determined using (31)P-NMR spectroscopy. Exposure to tolbutamide did not alter the nucleotide triphosphate levels. Collectively, data from the present study demonstrate that prolonged exposure of beta cells to tolbutamide results in changes in flux through key enzymes involved in glucose metabolism that, in turn, may impact on glucose-induced insulin secretion.

High glucose increases extracellular matrix production in pancreatic stellate cells by activating the renin-angiotensin system

Pancreatic stellate cells (PSCs) are involved in pancreatic inflammation and fibrosis. Recent studies have shown that blocking the renin-angiotensin system (RAS) attenuates pancreatic inflammation and fibrosis. However, there are few data about the direct effects of high glucose on extracellular matrix (ECM) protein synthesis and angiotensin II (Ang II) induction in PSCs. PSCs were isolated from male Sprague-Dawley rats and cultured in medium containing 5.5 mM (LG group) or 27 mM D-glucose (HG group). Levels of Ang II and transforming growth factor-beta (TGF-beta) in culture media were measured and Ang II-positive cells were counted. We used real-time polymerase chain reaction (PCR) to detect Ang II receptor expression and Western blot analysis for the expression of ECM proteins such as connective-tissue growth factor (CTGF) and collagen type IV. Cells were also treated with an Ang II-receptor antagonist (candesartan, 10 microM) or angiotensin-converting enzyme (ACE) inhibitor (ramiprilat, 100 nM). Thymidine uptake by PSCs increased fourfold with high glucose treatment. Ang II levels and the proportion of Ang II-positive PSCs were significantly increased after 6 h under high-glucose conditions. TGF-beta concentrations also increased significantly with high glucose. After 72 h, the expression of CTGF and collagen type IV proteins in high-glucose cultures increased significantly and this increase was effectively attenuated by the candesartan or the ramiprilat. All together, high glucose induced PSCs proliferation and ECM protein synthesis, and these effects were attenuated by an Ang II-receptor antagonist. The data suggest that pancreatic inflammation and fibrosis aggravated by hyperglycemia, and Ang II play an important role in this pathogenesis.

Further insights into the role of angiotensin II in kidney development

Over the past decade, compelling studies have highlighted the fundamental role of the renin-angiotensin system (RAS) in renal development and long-term control of renal function and arterial pressure. The present review provides an update of the understanding of how the RAS controls nephrogenesis and nephrovascular development. In addition, the investigations linking the perinatal development of RAS inhibition-induced renal dysmorphology and establishment of adult blood pressure are discussed.

Insights into the role of anaplerosis in insulin secretion: A 13C NMR study

AIMS/HYPOTHESIS

Defining mechanisms and enzymatic paths critical to fuel-regulated insulin secretion are key goals of diabetes research. In this study, 13C-nuclear magnetic resonance spectroscopy and isotopomer analysis were used to investigate the link between insulin secretion and metabolic pathways associated with the tricarboxylic acid (TCA) cycle.

MATERIALS AND METHODS

To this end, four insulinoma cell lines (betaTC3, betaTC-tet, INS-1 [832/13], R7T1) and porcine islets were examined under a variety of culture conditions (i.e. presence vs absence of amino acids and sera, and low vs high glucose).

RESULTS

Glucose consumption, insulin release, and glutamate isotopomeric patterns were influenced by media complexity (e.g. PBS, plain culture media, fully supplemented culture media). The 13C-labelled metabolites increased with media complexity and increasing glucose concentration, with the notable exception of aspartate, which was always higher under low-glucose conditions. The 13C-glutamate isotopomeric fractions were fitted to metabolic models to estimate the relative metabolic fluxes to the TCA cycle through key enzymatic processes. These indices of metabolism were compared with insulin secretion to determine correlative links. A model containing a single pool of pyruvate, an entrance to the TCA cycle via the pyruvate dehydrogenase complex, and two anaplerotic entrances, one through pyruvate carboxylase and another through an undefined (by the modelling program) source, provided the best fit to the data under all conditions tested, for all cell lines.

CONCLUSIONS/INTERPRETATION

On the basis of our findings, a strong correlation may exist between stimulated insulin secretion and non-pyruvate carboxylase anaplerosis for the four cell lines examined in this study.

Simvastatin attenuates hypertrophic responses induced by cardiotrophin-1 via JAK–STAT pathway in cultured cardiomyocytes

Cardiotrophin-1 (CT-1) is a cytokine involved in the growth and survival of cardiac cells via activation of the Janus activated kinase/signal transducer activator of transcription (JAK/STAT). Statins, 3-Hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitors, have effects that extend beyond cholesterol reduction and inhibit vascular smooth muscle cell (VSMC) proliferation and cardiac hypertrophy. However, whether stains also can inhibitin vitromyocardial hypertrophy or not still remains elusive. The purpose of this study was to explore the effects of simvastatin on the hypertrophy of cultured rat cardiomyocytes induced by CT-1 and to investigate whether this effect was mediated via JAK-STAT signaling pathway.

METHODS AND RESULTS

Primary cardiomyocytes from 2-day-old (P2) rats were cultured, stimulated with CT-1, and treated with various concentration of simvastatin. Incorporation of [(3)H] leucine, reverse transcription-polymerase chain reaction and western blotting techniques were used to investigate cardiacmyocyte size, ANP mRNA and JAK-STAT protein expression. Simvastatin was proved, in a dose-independent manner, to decrease cardiacmyocytes size as well as protein synthesis, and inhibit ANP mRNA synthesis and JAK-STAT protein expression induced by CT-1 in cardiacmyocytes.

CONCLUSION

These results suggest that simvastatin can ameliorate cardiacmyocytes hypertrophyin vitrovia JAK-STAT signaling pathways. The present study provides a novel understanding and alternative therapeutic strategy for cardiac hypertrophy.

Renal Protective Effects of the Renin-Angiotensin-Aldosterone System Blockade: From Evidence-Based Approach to Perspectives

The renin-angiotensin-aldosterone system (RAAS) blockade is currently the best-documented treatment strategy to delay the progression of chronic nephropathies. Angiotensin-converting enzyme inhibitors (CEIs) or angiotensin II type 1 receptor antagonists (ARBs) should be used in every normotensive and hypertensive patient with chronic proteinuric nephropathy of both diabetic and non-diabetic origin. The therapy should be initiated as early as possible, bearing in mind that the renoprotection is more effective if used before overt proteinuria or a reduction in kidney function is present. The therapy should be offered to all patients, regardless of renal function, as well as to subjects with severely impaired glomerular filtration. CEIs and ARBs should be administered in therapeutic doses as high as possible to achieve maximal possible proteinuria reduction and systemic blood pressure target <130/80 mm Hg, and 125/75 mm Hg in those subjects with renal insufficiency who present with proteinuria above 1 g/24 h. The combined therapy with the concomitant use of CEIs and ARBs should be offered to all patients with proteinuric non-diabetic chronic nephropathies who do not achieve full and persistent remission of proteinuria with CEI or ARB alone. The article reviews an evidence-based approach on the use of RAAS-inhibiting agents in kidney diseases, considers treatment strategies in different clinical situations and discusses some perspectives related to the implementation of the RAAS blockade in renal protection.

Decreased contractile and metabolic reserve in peroxisome proliferator-activated receptor-alpha-null hearts can be rescued by increasing glucose transport and utilization

BACKGROUND

Downregulation of peroxisome proliferator-activated receptor-alpha (PPARalpha) in hypertrophied and failing hearts leads to the reappearance of the fetal metabolic pattern, ie, decreased fatty acid oxidation and increased reliance on carbohydrates. Here, we sought to elucidate the functional significance of this shift in substrate preference.

METHODS AND RESULTS

We assessed contractile function and substrate utilization using 13C nuclear magnetic resonance spectroscopy and high-energy phosphate metabolism using 31P nuclear magnetic resonance spectroscopy in perfused hearts isolated from genetically modified mice (PPARalpha(-/-)) that mimic the metabolic profile in myocardial hypertrophy. We found that the substrate switch from fatty acid to glucose (3-fold down) and lactate (3-fold up) in PPARalpha(-/-) hearts was sufficient for sustaining normal energy metabolism and contractile function at baseline but depleted the metabolic reserve for supporting high workload. Decreased ATP synthesis (measured by 31P magnetization transfer) during high workload challenge resulted in progressive depletion of high-energy phosphate content and failure to sustain high contractile performance. Interestingly, the metabolic and functional defects in PPARalpha(-/-) hearts could be corrected by overexpressing the insulin-independent glucose transporter GLUT1, which increased the capacity for glucose utilization beyond the intrinsic response to PPARalpha deficiency.

CONCLUSIONS

These findings demonstrate that metabolic remodeling in hearts deficient in PPARalpha increases the susceptibility to functional deterioration during hemodynamic overload. Moreover, our results suggest that normalization of myocardial energetics by further enhancing myocardial glucose utilization is an effective strategy for preventing the progression of cardiac dysfunction in hearts with impaired PPARalpha activity such as hearts with pathological hypertrophy.

Modulation of cell proliferation and hypertrophy by gangliosides in cultured human glomerular mesangial cells

Glomerular mesangial cells (GMCs) in diverse renal diseases undergo cell proliferation and/or hypertrophy, and gangliosides have been reported to play an important role in modulating cell structure and function. This study compared the effects of transforming growth factor-beta1 (TGF-beta1) and the effects of the application of exogenous gangliosides on GMCs and investigated whether the application of exogenous gangliosides regulated cellular proliferation and hypertrophy. Human GMCs were cultured with exogenous gangliosides and TGF-beta1 in a media containing 10% fetal bovine serum and in a media without the fetal bovine serum. Exogenous gangliosides biphasically changed the proliferation of human GMCs (0.1-1.0 mg/mL). A low concentration (0.1 mg/mL) of gangliosides mainly increased the number of human GMCs, whereas cellular proliferation was significantly reduced by raising the concentration of exogenous gangliosides. TGF-beta1 greatly reduced the number of human GMCs in a concentration-dependent manner (1-10 ng/mL). Serum deprivation accelerated the gangliosides- and TGF-beta1-induced inhibition of mesangial cell proliferation to a greater extent. Gangliosides (1.0 mg/ mL) and TGF-beta1 (10 ng/mL) both caused a significant increase in the incorporation of [3H]leucine per cell in the serum-deprived condition, whereas it was completely reversed in serum-supplemented condition. Similar results to the [3H]leucine incorporation were also observed in the changes in cell size measured by flow cytometric analysis. These results show that exogenous gangliosides modulate cell proliferation and hypertrophy in cultured human GMCs, and these cellular responses were regulated differently based on whether the media contained serum or not. Results from the present study raise new possibilities about the potential involvement of gangliosides in the development of mesangial cell proliferation and hypertrophy.

Role of reactive oxygen species in angiotensin II-mediated renal growth, differentiation, and apoptosis

Angiotensin II (ANG II) induces cell-cycle arrest of cultured proximal tubular cells, resulting in cellular hypertrophy. This ANG II-mediated hypertrophy is associated with the induction of p27(Kip1), an inhibitor of G1 phase cyclin-dependent kinase cyclin complexes. We have recently demonstrated that ANG II-mediated expression of p27(Kip1) and induction of cellular hypertrophy depend on the generation of reactive oxygen species (ROS). The effects of ROS are mediated by stimulation of mitogen-activated protein (MAP) kinases. p44/42 MAP kinase directly phosphorylates p27(Kip1) at serine-threonine residues and increases thereby its half-life time. AT2-receptor activation has been implicated in apoptosis and/or cell differentiation. Recent studies, however, revealed a more indirect role of hypoxia in the antiproliferative effects of ANG II transduced through AT2 receptors. We found that SM-20 is down-regulated in ANG II-stimulated PC12 cells that express only AT2 receptors. It turned out that SM20 is the rat homologue of a dioxygenase that regulates hypoxia-inducible factor 1 (HIF-1). ANG II induces HIF-1alpha by a posttranscriptional mechanism suggesting that SM20 down-regulation leads to stabilization of HIF-1. Thus, ANG II-induced ROS generation plays a pivotal role in several pathophysiological situations, leading to renal growth regulation and remodeling after injury.

13C NMR isotopomer analysis of anaplerotic pathways in INS-1 cells

Anaplerotic flux into the Kreb's cycle is crucial for glucose-stimulated insulin secretion from pancreatic beta-cells. However, the regulation of flux through various anaplerotic pathways in response to combinations of physiologically relevant substrates and its impact on glucose-stimulated insulin secretion is unclear. Because different pathways of anaplerosis generate distinct products, they may differentially modulate the insulin secretory response. To examine this question, we applied 13C-isotopomer analysis to quantify flux through three anaplerotic pathways: 1) pyruvate carboxylase of pyruvate derived from glycolytic sources; 2) pyruvate carboxylase of pyruvate derived from nonglycolytic sources; and 3) glutamate dehydrogenase (GDH). At substimulatory glucose, anaplerotic flux rate in the clonal INS-1 832/13 cells was approximately 40% of Kreb's cycle flux, with similar contributions from each pathway. Increasing glucose to 15 mm stimulated insulin secretion approximately 4-fold, and was associated with a approximately 4-fold increase in anaplerotic flux that could mostly be attributed to an increase in PC flux. In contrast, the addition of glutamine to the perfusion media stimulated GDH flux approximately 6-fold at both glucose concentrations without affecting insulin secretion rates. In conclusion, these data support the hypothesis that a signal generated by anaplerosis from increased pyruvate carboxylase flux is essential for glucose-stimulated insulin secretion in beta-cells and that anaplerosis through GDH does not play a major role in this process.

Biochemical mechanism of lipid-induced impairment of glucose-stimulated insulin secretion and reversal with a malate analogue

Hyperlipidemia appears to play an integral role in loss of glucose-stimulated insulin secretion (GSIS) in type 2 diabetes. This impairment can be simulated in vitro by chronic culture of 832/13 insulinoma cells with high concentrations of free fatty acids, or by study of lipid-laden islets from Zucker diabetic fatty rats. Here we show that impaired GSIS is not a simple result of saturation of lipid storage pathways, as adenovirus-mediated overexpression of a cytosolically localized variant of malonyl-CoA decarboxylase in either cellular model results in dramatic lowering of cellular triglyceride stores but no improvement in GSIS. Instead, the glucose-induced increment in "pyruvate cycling" activity (pyruvate exchange with tricarboxylic acid cycle intermediates measured by (13)C NMR), previously shown to play an important role in GSIS, is completely ablated in concert with profound suppression of GSIS in lipid-cultured 832/13 cells, whereas glucose oxidation is unaffected. Moreover, GSIS is partially restored in both lipid-cultured 832/13 cells and islets from Zucker diabetic fatty rats by addition of a membrane permeant ester of a pyruvate cycling intermediate (dimethyl malate). We conclude that chronic exposure of islet beta-cells to fatty acids grossly alters a mitochondrial pathway of pyruvate metabolism that is important for normal GSIS.

A novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in rat vascular smooth muscle and renal proximal tubular cells

Angiotensin II stimulates cellular hypertrophy in cultured vascular smooth muscle and renal proximal tubular cells. This effect is believed to be one of earliest morphological changes of heart and renal failure. However, the precise molecular mechanism involved in angiotensin II-induced hypertrophy is poorly understood. In the present study we report the isolation of a novel angiotensin II type 1 receptor-associated protein. It encodes a 531-amino acid protein. Its mRNA is detected in all human tissues examined but highly expressed in the human kidney, pancreas, heart, and human embryonic kidney cells as well as rat vascular smooth muscle and renal proximal tubular cells. Protein synthesis and relative cell size analyzed by flow cytometry studies indicate that overexpression of the novel angiotensin II type 1 receptor-associated protein induces cellular hypertrophy in cultured rat vascular smooth muscle and renal proximal tubular cells. In contrast, the hypertrophic effects was reversed in renal proximal tubular cell lines expressing the novel gene in the antisense orientation and its dominant negative mutant, which lacks the last 101 amino acids in its carboxyl-terminal tail. The hypertrophic effects are at least in part mediated via protein kinase B activation or cyclin-dependent kinase inhibitor, p27(kip1) protein expression level in vascular smooth muscle, and renal proximal tubular cells. Moreover, angiotensin II could not stimulate cellular hypertrophy in renal proximal tubular cells expressing the novel gene in the antisense orientation and its mutant. These findings may provide new molecular mechanisms to understand hypertrophic agents such as angiotensin II-induced cellular hypertrophy.

Angiotensin II's antiproliferative effects mediated through AT2-receptors depend on down-regulation of SM-20

Angiotensin II (ANG II) inhibits proliferation and induces differentiation through AT2 receptors. However, target genes involved in this process are not well characterized. We studied PC12 cells, a rat pheochromocytoma cell line exclusively expressing AT2 receptors. ANG II attenuated proliferation of PC12 cells without concomitant induction of apoptosis. To identify potential novel genes involved in the antimitogenic actions of ANG II, we performed differential display analysis of PC12 cells after challenge with 10(-7) M ANG II for 6 hours. One identified gene selected for further study that was down-regulated by ANG II in PC12 cells was SM-20. This gene has been previously isolated from vascular smooth muscle cells treated with mitogens by differential hybridization. Recent findings show a homology of SM-20 with enzymes involved in the regulation of hypoxia inducible factor 1. ANG II suppressed mRNA expression of SM-20 in PC12 cells after only 30 minutes, as detected by Northern blotting. This effect was antagonized by an AT2 receptor blocker, but not by losartan. A rabbit polyclonal antibody was generated against a peptide sequence of SM-20 and detected a major band of the predicted size of 40 kd and a second 33-kd band that likely represents a processed form present in mitochondria. Immunohistochemistry revealed a granular staining of the cytoplasm of PC12 cells compatible with a previously described mitochondrial localization of SM-20 protein. Western blots confirmed the down-regulation of SM-20 protein in PC12 cells subsequent to incubation with ANG II. SM-20 transcripts were also reduced by ANG II acting on AT2 receptors in rat glomerular endothelial cells that express both AT1 and AT2 receptors. SM-20 antisense, but not sense, phosphothioate-modified oligonucleotides reduced base-line proliferation of PC12 cells. In contrast, inducible overexpression of SM-20 using the ecdysone system prevented the antiproliferative effects of ANG II in PC12 cells. In summary, our study identified SM-20 as an essential component of ANG II's growth-suppressive effects mediated through AT2 receptors. This gene apparently plays an important role in the regulatory processes determining whether a cell should undergo differentiation, apoptosis, or proliferation.

Modulation of cardiac PIP2 by cardioactive hormones and other physiologically relevant interventions

Phosphatidylinositol 4,5-bisphosphate (PIP2) affects profoundly several cardiac ion channels and transporters, and studies of PIP2-sensitive currents in excised patches suggest that PIP2 can be synthesized and broken down within 30 s. To test when, and if, total phosphatidylinositol 4-phosphate (PIP) and PIP(2) levels actually change in intact heart, we used a new, nonradioactive HPLC method to quantify anionic phospholipids. Total PIP and PIP2 levels (10-30 micromol/kg wet weight) do not change, or even increase, with activation of Galpha(q)/phospholipase C (PLC)-dependent pathways by carbachol (50 microM), phenylephrine (50 microM), and endothelin-1 (0.3 microM). Adenosine (0.2 mM) and phorbol 12-myristate 13-acetate (1microM) both cause 30% reduction of PIP2 in ventricles, suggesting that diacylglycerol (DAG)-dependent mechanisms negatively regulate cardiac PIP2. PIP2, but not PIP, increases reversibly by 30% during electrical stimulation (2 Hz for 5 min) in guinea pig left atria; the increase is blocked by nickel (2 mM). Both PIP and PIP2 increase within 3 min in hypertonic solutions, roughly in proportion to osmolarity, and similar effects occur in multiple cell lines. Inhibitors of several volume-sensitive signaling mechanisms do not affect these responses, suggesting that PIP2 metabolism might be sensitive to membrane tension, per se.

13C NMR isotopomer analysis reveals a connection between pyruvate cycling and glucose-stimulated insulin secretion (GSIS)

Cellular metabolism of glucose is required for stimulation of insulin secretion from pancreatic beta cells, but the precise metabolic coupling factors involved in this process are not known. In an effort to better understand mechanisms of fuel-mediated insulin secretion, we have adapted 13C NMR and isotopomer methods to measure influx of metabolic fuels into the tricarboxylic acid (TCA) cycle in insulinoma cells. Mitochondrial metabolism of [U-13C3]pyruvate, derived from [U-13C6]glucose, was compared in four clonal rat insulinoma cell 1-derived cell lines with varying degrees of glucose responsiveness. A 13C isotopomer analysis of glutamate isolated from these cells showed that the fraction of acetyl-CoA derived from [U-13C6]glucose was the same in all four cell lines (44 +/- 5%, 70 +/- 3%, and 84 +/- 4% with 3, 6, or 12 mM glucose, respectively). The 13C NMR spectra also demonstrated the existence of two compartmental pools of pyruvate, one that exchanges with TCA cycle intermediates and a second pool derived from [U-13C6]glucose that feeds acetyl-CoA into the TCA cycle. The 13C NMR spectra were consistent with a metabolic model where the two pyruvate pools do not randomly mix. Flux between the mitochondrial intermediates and the first pool of pyruvate (pyruvate cycling) varied in proportion to glucose responsiveness in the four cell lines. Furthermore, stimulation of pyruvate cycling with dimethylmalate or its inhibition with phenylacetic acid led to proportional changes in insulin secretion. These findings indicate that exchange of pyruvate with TCA cycle intermediates, rather than oxidation of pyruvate via acetyl-CoA, correlates with glucose-stimulated insulin secretion.

Nonradioactive analysis of phosphatidylinositides and other anionic phospholipids by anion-exchange high-performance liquid chromatography with suppressed conductivity detection

Phosphatidylinositol 4,5-biphosphate (PIP(2)) modulates the function of numerous ion transporters and channels, as well as cell signaling and cytoskeletal proteins. To study PIP(2) levels of cells without radiolabeling, we have developed a new method to quantify anionic phospholipid species. Phospholipids are extracted and deacylated to glycero-head groups, which are then separated by anion-exchange HPLC and detected by suppressed conductivity measurements. The major anionic head groups can be quantified in single runs with practical detection limits of about 100 pmol, and the D3 isoforms of phosphatidylinositol phosphate (PIP) and PIP(2) are detected as shoulder peaks. In HeLa, Hek 293 and COS cells, as well as intact heart, PIP(2) amounts to 0.5 to 1.5% of total anionic phospholipid (10 to 30 micromol/liter cell water or 0.15 to 0.45 nmol/mg protein). In cell cultures, overexpression of Type I PIP5-kinase specifically increases PIP(2), whereas overexpression of Type II PI4-kinase can increase both PIP and PIP(2). Phosphatidylinositol 3,4,5-trisphosphate (PIP(3)) and the D3 isomers of PIP(2) are detected after treatment of cells with pervanadate; in yeast, overexpression of a phosphatidylinositol 3-kinase (VPS34) specifically increases phosphatidylinositol 3-phosphate (PI3P). Using isolated cardiac membranes, lipid kinase and lipid phosphatase activities can be monitored with the same methods. Upon addition of ATP, PIP increases while PIP(2) remains low; exogenous PIP(2) is rapidly degraded to PIP and phosphatidylinositol (PI). In summary, the HPLC methods described here can be used to probe multiple aspects of phosphatidylinositide (Ptide) metabolism without radiolabeling.