Luminometric assays of ATP, phosphocreatine, and creatine for estimation of free ADP and free AMP

Stabilization Effects Induced by Trehalose on Creatine Aqueous Solutions Investigated by Infrared Spectroscopy

Creatine is a very popular amino acid widely utilized in the sports world due to its functions mainly related to muscle building and increasing performance. The present work investigates the behavior of creatine aqueous solutions and of creatine aqueous in the presence of trehalose as a function of time changes by means of Infrared spectroscopy. Infrared spectra have been gathered and studied over time for both the full spectrum and the intramolecular OH-stretching region for the two mixtures. This latter region was studied more specifically using a cutting-edge technique called Spectral Distance (SD). From this analysis of the spectral features of the investigated samples, it emerges that trehalose has a significant stabilizing effect on creatine aqueous solutions.

Highly sensitive detection of Tb3+ and ATP based on a novel asymmetric anthracene derivative

A novel fluorescent sensor based on an asymmetric anthracene derivative (SSAPA) was designed and synthesized. Using this molecule, a rapid and sensitive assay for detecting Tb³⁺ and ATP in aqueous solutions was established. The SSAPA molecule had excellent aggregation-induced emission (AIE) performance and good aqueous dispersion ability. This molecule could coordinate with Tb³⁺ and the fluorescence quenched linearly with the increase in the concentration of Tb³⁺ from 0.005 to 1.2 μM. Since both Tb³⁺ and adenosine triphosphate (ATP) have strong binding ability, ATP can compete with Tb³⁺ from the SSAPA/Tb³⁺ complex leading to fluorescence recovery. In this way, a brand-new fluorescent "turn-on" assay for ATP in the range from 0.01 to 0.4 μM was developed using the Tb³⁺-based complex probe. The detection limits for Tb³⁺ and ATP both reached single-digit nanomole per millilitre (2.8 nM and 4.5 nM, respectively), which demonstrated that this method has high sensitivity. Besides, Tb³⁺ and ATP also could be well detected in other complex environments such as real water samples or serum samples. This study provides a feasible assay for detecting trace amounts of Tb³⁺ and ATP in aqueous solutions.

ATP Redux

The renaissance of interest in metabolism has focused mostly on techniques to measure massive numbers of metabolites. Yet, established metabolic theory has been abandoned. Here, I highlight one misconception: how ATP (and ADP and AMP) are currently understood. A critical point was established early on: cellular [ATP] is constant.

Inhibition of glycolysis by targeting lactate dehydrogenase A facilitates hyaluronan synthase 2 synthesis in synovial fibroblasts of temporomandibular joint osteoarthritis

OBJECTIVE

Although associations between dysregulated glucose metabolism and human rheumatoid arthritis have been reported, the disturbance and influence of glycolytic metabolism on temporomandibular joint osteoarthritis remains unclear. This study aimed to investigate the expression level and metabolite profile of the critical glycolytic enzyme, lactate dehydrogenase A (LDHA) in synovial fibroblasts (SFs) of TMJOA, assess the effect of glycolytic inhibition on synthesis of hyaluronan synthase 2 (HAS2) and inflammation progression in these cells.

METHODS

Immunohistochemistry and western blotting were performed to detect the expression of LDHA in the lining and sub-lining layers of synovial tissue and SFs. MTT and EdU assays were used to measure the cell proliferation. The cell apoptosis were demonstrated by TUNEL staining and Annexin V/PI double staining. A potent and specific inhibitor of LDHA, GSK2837808A, was administrated to suppress the activity of LDHA and detect the potential efficacy on HAS2.

RESULTS

LDHA expression was dramatically higher in the synovial tissue and SFs from TMJOA patients compared to control groups. LDHA inhibition impaired active LDHA performance, suppressed the glucose uptake and decreased lactate concentration. Furthermore, GSK2837808A reversed the occurrence of low ratio of ATP/AMP, high level of Adenosine Monophosphate-activated Protein Kinase (AMPK) activation, disturbed HAS2 synthesis and hyaluronic acid (HA) production by inhibiting LDHA. The cellular viability and cell cycle were not affected by GSK2837808A at the working concentration.

CONCLUSIONS

Targeting LDHA using its specific suppressant GSK2837808A impeded lactate secretion and contributed to HAS2 and HA synthesis in TMJOA SFs, providing the vital role of LDHA associated with TMJOA pathogenesis and a novel therapeutic approach for TMJOA.

Efficacy of an adenosine triphosphate meter for evaluating caries risk in clinical dental practice

BACKGROUND

Adenosine triphosphate bioluminescence (ATP-B) readings have been proposed as markers of caries risk. ATP readings may indicate bacteria or oral streptococci activity in microbial plaque. The authors of this study aimed to evaluate whether readings using a commercial ATP meter (CariScreen Testing Meter, Oral BioTech) are significantly different for patients with low, moderate, and high caries risk in the Caries Management by Risk Assessment Practice-Based Research Network study.

METHODS

Twenty practice-based research network dentists enrolled 460 patients; 271 returned for 2 or more semiannual follow-up visits over 2 years. Dentists were trained and calibrated to perform ATP-B testing and caries risk assessment (CRA) using established protocols. ATP-B readings were compared via CRA category (low, moderate, high). Generalized estimating equations were used to compare the risk of experiencing incident clinical outcomes (newly recorded decayed, missing, or restored tooth surfaces and CRA disease indicators) according to ATP-B reading at prior patient visits (≥ 1,500 versus < 1,500 relative light units).

RESULTS

Median ATP-B readings did not differ statistically significantly by clinician-assessed caries risk level (low, 2,323; moderate, 2,940; high, 3,217; P = .65). Adjusted for patient demographics and trial intervention assignment, higher readings were not associated with newly developed decayed, missing, or restored tooth surface (relative risk, 1.57; 95% confidence interval, 0.55 to 4.45) or disease indicators (relative risk, 1.08; 95% confidence interval, 0.85 to 1.37) at the following visit, whereas clinician-assessed caries risk level was strongly associated.

CONCLUSIONS

ATP-B readings poorly predicted caries risk and future clinical outcomes. CRA incorporating multiple risk, protective, and disease indicators has superior predictive performance.

PRACTICAL IMPLICATIONS

The findings of this study do not provide evidence supporting the use of ATP-B to predict caries risk.

Control of pancreatic β-cell bioenergetics

The canonical model of glucose-stimulated insulin secretion (GSIS) by pancreatic β-cells predicts a glucose-induced rise in the cytosolic ATP/ADP ratio. Such bioenergetic sensitivity to metabolic fuel is unusual as it implies that ATP flux is governed, to a significant extent, by ATP supply, while it is predominantly demand-driven in other cell types. Metabolic control is generally shared between different processes, but potential control of ATP consumption over β-cell bioenergetics has been largely ignored to date. The present paper offers a brief overview of experimental evidence that demonstrates ATP flux control by glucose-fuelled oxidative phosphorylation. Based on old and new data, it is argued that ATP supply does not hold exclusive control over ATP flux, but shares it with ATP demand, and that the distribution of control is flexible. Quantification of the bioenergetic control distribution will be important from basic and clinical perspectives, but precise measurement of the cytosolic ATP/ADP ratio is complicated by adenine nucleotide compartmentalisation. Metabolic control analysis of β-cell bioenergetics will likely clarify the mechanisms by which glucose and fatty acids amplify and potentiate GSIS, respectively. Moreover, such analysis may offer hints as to how ATP flux control shifts from ATP supply to ATP demand during the development of type 2 diabetes, and why prolonged sulfonylurea treatment causes β-cell deterioration.

The Pancreatic β-Cell: A Bioenergetic Perspective

The pancreatic β-cell secretes insulin in response to elevated plasma glucose. This review applies an external bioenergetic critique to the central processes of glucose-stimulated insulin secretion, including glycolytic and mitochondrial metabolism, the cytosolic adenine nucleotide pool, and its interaction with plasma membrane ion channels. The control mechanisms responsible for the unique responsiveness of the cell to glucose availability are discussed from bioenergetic and metabolic control standpoints. The concept of coupling factor facilitation of secretion is critiqued, and an attempt is made to unravel the bioenergetic basis of the oscillatory mechanisms controlling secretion. The need to consider the physiological constraints operating in the intact cell is emphasized throughout. The aim is to provide a coherent pathway through an extensive, complex, and sometimes bewildering literature, particularly for those unfamiliar with the field.

The brain metabolic activity after resuscitation with liposome-encapsulated hemoglobin in a rat model of hypovolemic shock

We examined the effect of resuscitation with liposome-encapsulated hemoglobin (LEH) on cerebral bioenergetics in a rat model of 45% hypovolemia. The rats were resuscitated with isovolemic LEH or saline after 15 minutes of shock and followed up to 6 hours. Untreated hypovolemic rats received no fluid. The cerebral uptake of F-18-fluorodeoxyglucose (FDG) was measured by PET, and at 6 hours, the brain was collected for various assays. Hypovolemia decreased cellular adenosine triphosphate (ATP), phosphocreatine, nicotinamide adenine dinucleotide (NAD)/NADH ratio, citrate synthase activity, glucose-6-phosphate, and nerve growth factor (NGF), even when FDG uptake remained unchanged. The FDG uptake was reduced by saline, but not by LEH infusion. The reduced FDG uptake in saline group was associated with a decrease in hexokinase I expression. The LEH infusion effectively restored ATP content, NAD/NADH ratio, and NGF expression, and reduced the hypovolemia-induced accumulation of pyruvate and ubiquitinated proteins; in comparison, saline was significantly less effective. The LEH infusion was associated with low pH and high anion gap, indicating anionic gap acidosis. The results suggest that hypovolemic shock perturbs glucose metabolism at the level of pyruvate utilization, resulting in deranged cerebral energy stores. The correction of volume and oxygen deficits by LEH recovers the cerebral metabolism and creates a prosurvival phenotype.

Hemorrhagic shock-induced cerebral bioenergetic imbalance is corrected by pharmacologic treatment with EF24 in a rat model

Maintenance of cerebral viability and function is an important goal of critical care in victims of injury due to ischemia and hypovolemia. As part of the multiple organ dysfunction syndrome, the brain function after trauma is influenced by the systemic inflammatory response. We investigated the effect of EF24, an anti-inflammatory bis-chalcone, on cerebral bioenergetics in a rat model of 45% hemorrhagic shock. The rats were treated with EF24 (0.4 mg/kg) or EF24 with an artificial oxygen carrier liposome-encapsulated hemoglobin (LEH). The volume of LEH administered was equal to the shed blood. The brain was collected after 6 h of shock for biochemical assays. EF24 treatment showed significant recovery of ATP, phosphocreatine, and NAD/NADH ratio. It also increased citrate synthase activity and cytochrome c oxidase subunit IV expression which were reduced in shock brain. Furthermore, it reduced the shock-induced accumulation of pyruvate and pyruvate dehydrogenase kinase-1 expression, suggesting that EF24 treatment improves cerebral energetics by restoring perturbed pyruvate metabolism in the mitochondria. These effects of EF24 were associated with reduced poly(ADP-ribose) polymerase cleavage and a significant improvement in the levels of nerve growth factor and brain-derived neurotrophic factor in shock brain. Co-administration of LEH with EF24 was only marginally more effective as compared to the treatment with EF24 alone. These results show that EF24 treatment sets up a pro-survival phenotype in shock by resurrecting cerebral bioenergetics. Since EF24 was effective in the absence of accompanying fluid resuscitation, it has potential utility as a pre-hospital pharmacotherapy in shock due to accidental blood loss.

Spectroscopic study of the interaction between adenosine disodium triphosphate and gatifloxacin-Al3+ complex and its analytical application

A new and sensitive spectrofluorimetric method has been proposed to determine trace amount of adenosine disodium triphosphate (ATP). The method is based on the fluorimetric interaction between gatifloxacin (GFLX)-aluminium (III) (Al(3+) ) complex and ATP and studied using UV-visible and fluorescence spectroscopy. Weak luminescence spectra of Al(3+) were enhanced after complexation with GFLX at 423 nm upon excitation at 272 nm due to energy transfer from the ligand to the Al(3+) ion. It was observed that the FL emission spectrum of GFLX-Al(3+) was enhanced significantly by the addition of ATP. Under the optimal conditions, the enhancement of FL intensity at 423 nm was responded linearly with the concentration of ATP in the range 1.3 × 10(-10) - 1.0 × 10(-8) mol L(-1) with correlation coefficient (r) of 0.9981. The limit of detection (LOD) was found to be 1.1 × 10(-11) mol L(-1) for ATP with the standard deviation (RSD) of 1.21% for five repeated measurement of 2.3 × 10(-8) mol L(-1) ATP. The presented method is simple, sensitive, free from coexisting interferents and can be applied successfully to determine ATP in the real samples.

Skeletal muscle ATP kinetics are impaired in frail mice

The interleukin-10 knockout mouse (IL10(tm/tm)) has been proposed as a model for human frailty, a geriatric syndrome characterized by skeletal muscle (SM) weakness, because it develops an age-related decline in SM strength compared to control (C57BL/6J) mice. Compromised energy metabolism and energy deprivation appear to play a central role in muscle weakness in metabolic myopathies and muscular dystrophies. Nonetheless, it is not known whether SM energy metabolism is altered in frailty. A combination of in vivo (31)P nuclear magnetic resonance experiments and biochemical assays was used to measure high-energy phosphate concentrations, the rate of ATP synthesis via creatine kinase (CK), the primary energy reserve reaction in SM, as well as the unidirectional rates of ATP synthesis from inorganic phosphate (Pi) in hind limb SM of 92-week-old control (n = 7) and IL10(tm/tm) (n = 6) mice. SM Phosphocreatine (20.2 ± 2.3 vs. 16.8 ± 2.3 μmol/g, control vs. IL10(tm/tm), p < 0.05), ATP flux via CK (5.0 ± 0.9 vs. 3.1 ± 1.1 μmol/g/s, p < 0.01), ATP synthesis from inorganic phosphate (Pi → ATP) (0.58 ± 0.3 vs. 0.26 ± 0.2 μmol/g/s, p < 0.05) and the free energy released from ATP hydrolysis (∆G ∼ATP) were significantly lower and [Pi] (2.8 ± 1.0 vs. 5.3 ± 2.0 μmol/g, control vs. IL10(tm/tm), p < 0.05) markedly higher in IL10(tm/tm) than in control mice. These observations demonstrate that, despite normal in vitro metabolic enzyme activities, in vivo SM ATP kinetics, high-energy phosphate levels and energy release from ATP hydrolysis are reduced and inorganic phosphate is elevated in a murine model of frailty. These observations do not prove, but are consistent with the premise, that energetic abnormalities may contribute metabolically to SM weakness in this geriatric syndrome.

Genome-wide expression profiling and functional characterization of SCA28 lymphoblastoid cell lines reveal impairment in cell growth and activation of apoptotic pathways

Background

SCA28 is an autosomal dominant ataxia associated with AFG3L2 gene mutations. We performed a whole genome expression profiling using lymphoblastoid cell lines (LCLs) from four SCA28 patients and six unrelated healthy controls matched for sex and age.

Methods

Gene expression was evaluated with the Affymetrix GeneChip Human Genome U133A 2.0 Arrays and data were validated by real-time PCR.

Results

We found 66 genes whose expression was statistically different in SCA28 LCLs, 35 of which were up-regulated and 31 down-regulated. The differentially expressed genes were clustered in five functional categories: (1) regulation of cell proliferation; (2) regulation of programmed cell death; (3) response to oxidative stress; (4) cell adhesion, and (5) chemical homeostasis. To validate these data, we performed functional experiments that proved an impaired SCA28 LCLs growth compared to controls (p < 0.005), an increased number of cells in the G0/G1 phase (p < 0.001), and an increased mortality because of apoptosis (p < 0.05). We also showed that respiratory chain activity and reactive oxygen species levels was not altered, although lipid peroxidation in SCA28 LCLs was increased in basal conditions (p < 0.05). We did not detect mitochondrial DNA large deletions. An increase of TFAM, a crucial protein for mtDNA maintenance, and of DRP1, a key regulator of mitochondrial dynamic mechanism, suggested an alteration of fission/fusion pathways.

Conclusions

Whole genome expression profiling, performed on SCA28 LCLs, allowed us to identify five altered functional categories that characterize the SCA28 LCLs phenotype, the first reported in human cells to our knowledge.

Metformin increases mitochondrial energy formation in L6 muscle cell cultures

A popular hypothesis for the action of metformin, the widely used anti-diabetes drug, is the inhibition of mitochondrial respiration, specifically at complex I. This is consistent with metformin stimulation of glucose uptake by muscle and inhibition of gluconeogenesis by liver. Yet, mitochondrial inhibition is inconsistent with metformin stimulation of fatty acid oxidation in both tissues. In this study, we measured mitochondrial energy production in intact cells adapting an in vivo technique of phosphocreatine (PCr) formation following energy interruption ("PCr recovery") to cell cultures. Metformin increased PCr recovery from either dinitrophenol (DNP) or azide in L6 cells. We found that metformin alone had no effect on cell viability as measured by total ATP concentration, trypan blue exclusion, or 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction. However, treatments with low concentrations of DNP or azide reversibly decreased ATP concentration. Metformin increased 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction during recovery from either agent. Viability measured by trypan blue exclusion indicated that cells were intact under these conditions. We also found that metformin increased free AMP and, to a smaller extent, free ADP concentrations in cells, an action that was duplicated by a structurally unrelated AMP deaminase inhibitor. We conclude that, in intact cells, metformin can lead to a stimulation of energy formation, rather than an inhibition.

Creatine kinase overexpression improves ATP kinetics and contractile function in postischemic myocardium

Reduced myofibrillar ATP availability during prolonged myocardial ischemia may limit post-ischemic mechanical function. Because creatine kinase (CK) is the prime energy reserve reaction of the heart and because it has been difficult to augment ATP synthesis during and after ischemia, we used mice that overexpress the myofibrillar isoform of creatine kinase (CKM) in cardiac-specific, conditional fashion to test the hypothesis that CKM overexpression increases ATP delivery in ischemic-reperfused hearts and improves functional recovery. Isolated, retrograde-perfused hearts from control and CKM mice were subjected to 25 min of global, no-flow ischemia and 40 min of reperfusion while cardiac function [rate pressure product (RPP)] was monitored. A combination of (31)P-nuclear magnetic resonance experiments at 11.7T and biochemical assays was used to measure the myocardial rate of ATP synthesis via CK (CK flux) and intracellular pH (pH(i)). Baseline CK flux was severalfold higher in CKM hearts (8.1 ± 1.0 vs. 32.9 ± 3.8, mM/s, control vs. CKM; P < 0.001) with no differences in phosphocreatine concentration [PCr] and RPP. End-ischemic pH(i) was higher in CKM hearts than in control hearts (6.04 ± 0.12 vs. 6.37 ± 0.04, control vs. CKM; P < 0.05) with no differences in [PCr] and [ATP] between the two groups. Post-ischemic PCr (66.2 ± 1.3 vs. 99.1 ± 8.0, %preischemic levels; P < 0.01), CK flux (3.2 ± 0.4 vs. 14.0 ± 1.2 mM/s; P < 0.001) and functional recovery (13.7 ± 3.4 vs. 64.9 ± 13.2%preischemic RPP; P < 0.01) were significantly higher and lactate dehydrogenase release was lower in CKM than in control hearts. Thus augmenting cardiac CKM expression attenuates ischemic acidosis, reduces injury, and improves not only high-energy phosphate content and the rate of CK ATP synthesis in postischemic myocardium but also recovery of contractile function.

Reexamination of magnetic isotope and field effects on adenosine triphosphate production by creatine kinase

The influence of isotopically enriched magnesium on the creatine kinase catalyzed phosphorylation of adenosine diphosphate is examined in two independent series of experiments where adenosine triphosphate (ATP) concentrations were determined by a luciferase-linked luminescence end-point assay or a real-time spectrophotometric assay. No increase was observed between the rates of ATP production with natural Mg, (24)Mg, and (25)Mg, nor was any significant magnetic field effect observed in magnetic fields from 3 to 1,000 mT. Our results are in conflict with those reported by Buchachenko et al. [J Am Chem Soc 130:12868-12869 (2008)], and they challenge these authors' general claims that a large (two- to threefold) magnetic isotope effect is "universally observable" for ATP-producing enzymes [Her Russ Acad Sci 80:22-28 (2010)] and that "enzymatic phosphorylation is an ion-radical, electron-spin-selective process" [Proc Natl Acad Sci USA 101:10793-10796 (2005)].

Energy metabolism in umbilical endothelial cells from preterm and term neonates

AIM

The aim of this study was to investigate the impact of gestational age on energy metabolism in human umbilical vein endothelial cells (HUVECs) of preterm and term neonates.

METHODS

Activities of respiratory chain (RC) complexes I-V, citrate synthase (CS), overall mitochondrial fatty acid oxidation (FAO), carnitine palmitoyltransferase 2 (CPT2), glycolytic enzymes as well as energy-rich phosphates in HUVECs from uncomplicated term and preterm pregnancies were measured. Neonatal acylcarnitine profiles were analyzed postpartum.

RESULTS

Activities of RC complexes II+III, IV, V, and CS were higher in HUVECs from immature pregnancies. Overall FAO did not change, whereas CPT2 activity was higher in term neonates. RC complexes II-V and CS correlated inversely to gestational age, as well as CPT2 activity within the term cohort. Phosphofructokinase activity increased with maturation; lactate dehydrogenase and hexokinase as well as energy-rich phosphates remained constant. In blood, long-chain acylcarnitines were higher in term neonates.

CONCLUSIONS

Gestational age-dependent differences of energy-providing pathways in HUVECs were shown. Alterations of RC complexes with gestational age may be an adaptive process to cope with metabolic stress during birth; reduced oxidative phosphorylation and high glycolytic activity make HUVECs less susceptible to peripartum hypoxic damage. We hypothesize that HUVECs of premature neonates are metabolically maladapted to birth, which may be responsible for perinatal complications.

Co-treatment with Shengmai San-derived herbal product ameliorates chronic ethanol-induced liver damage in rats

Wei Kang Su (WKS) is an antioxidant-enriched herbal product manufactured on the basis of Shengmai San, a well-known traditional Chinese herbal formula. In the present study, we investigated the effects of WKS co-treatment on chronic ethanol toxicity in rats. WKS co-treatment protected against chronic ethanol-induced hepatotoxicity, as evidenced by the suppression of plasma enzyme activities and reactive oxygen metabolite levels, as well as the inhibition of hepatic mitochondrial malondialdehyde production in chronic ethanol-intoxicated rats. The hepatoprotection afforded by WKS co-treatment in chronic ethanol-intoxicated rats was associated with a reversal of altered hepatic mitochondrial antioxidant status and adenosine triphosphate (ATP) generation capacity, as well as heat shock protein 25/70 production. Therefore, WKS may offer the prospect of preventing ethanol-associated liver damage by increasing the resistance of mitochondria to oxidative stress.

Long-term treatment with shengmai san-derived herbal supplement (Wei Kang Su) enhances antioxidant response in various tissues of rats with protection against carbon tetrachloride hepatotoxicity

Wei Kang Su (WKS) is a commercial herbal product based on a Chinese herbal formula, Shengmai San. Here, we investigated the effects of long-term treatment with WKS on mitochondrial antioxidant status and functional ability, as well as heat shock protein (Hsp) 25/70 production, in various tissues of rats. WKS treatment enhanced mitochondrial antioxidant status and ATP generation capacity, as well as Hsp 25/70 production in various rat tissues. WKS treatment suppressed plasma reactive oxygen metabolite levels and protected against carbon tetrachloride hepatotoxicity in rats. Long-term WKS treatment may prevent diseases by enhancing the resistance of mitochondria to oxidative stress.

Cyclosporine A: impact on mitochondrial function in endothelial cells

INTRODUCTION

Although cyclosporine A (CSA) is considered to be an efficient immunosuppressive compound in transplantation, vascular side effects like arterial hypertension, neurologic complications and other adverse reactions occur. Interference of CSA with mitochondrial function may be responsible for these side effects.

METHODS

We evaluated the effect of CSA on mitochondrial and glycolytic function by measuring fatty acid oxidation (FAO), activities of respiratory chain complexes (RC) and citratesynthase (CS), lactate/pyruvate-ratios, energy-rich phosphates as well as activities of some glycolytic enzymes in human umbilical vein endothelial cells.

RESULTS

After 48 h of CSA incubation, global FAO, RC-complexes 1 + 3; 4 and 5 as well as CS were compromised while energy charges were not reduced. Lactate/pyruvate-ratios increased; cellular lactate dehydrogenase (LDH)-, hexokinase- and phosphofructokinase-activities were not impaired by CSA. Moderate cellular toxicity, assessed by LDH leakage, appeared only at the highest CSA concentration.

CONCLUSION

Part of CSA toxicity may arise from alterations in mitochondrial function as judged by impaired FAO and respiratory chain enzymes. To some extent, energy balance seems to be maintained by cytosolic energy production. Although only demonstrated for endothelial cells, it is conceivable that such effects will alter energy metabolism of different organs with high oxidative energy demands.

A bioluminescent method for measuring thymidylate kinase activity suitable for high-throughput screening of inhibitor

Blocking human thymidylate kinase (TMPK) function has a chemosensitization effect in anticancer treatment. However, a rapid and sensitive TMPK activity assay method suitable for inhibitor screening has been lacking. We have designed a luciferase-coupled TMPK assay in which luminescence emission is proportional to the magnitude of TMPK inhibition. The advantages of using this new method over the conventional nicotinamide adenine dinucleotide (reduced form, NADH)-coupling method in screening inhibitor include low cost, low limit in detecting inhibitory signal, more accurate, and devoid of interference due to compound absorbance at 340 nm.

Abnormal energetics and ATP depletion in pressure-overload mouse hearts: in vivo high-energy phosphate concentration measures by noninvasive magnetic resonance

(31)P magnetic resonance spectroscopy (MRS) offers a unique means to noninvasively quantify the major cardiac high-energy phosphates, creatine phosphate (PCr) and adenosine 5'-triphosphate (ATP), that are critical for normal myocardial contractile function and viability. Spatially localized (31)P MRS has been used to quantify the in vivo PCr-to-ATP ratio (PCr/ATP) of murine hearts, including those with pressure-overload hypertrophy induced by thoracic aortic constriction (TAC). To date, there has been no approach for measuring the absolute tissue concentrations of PCr and ATP in the in vivo mouse heart that promise a better understanding of high-energy metabolism. A method to quantify in vivo murine myocardial concentrations of PCr and ATP using an external reference is described, validated, and applied to normal and TAC hearts. This new method does not prolong the scan times in mice beyond those previously required to measure PCr/ATP. The new method renders an [ATP] of 5.0 +/- 0.9 (mean +/- SD) and [PCr] of 10.4 +/- 1.4 micromol/g wet wt in normal mouse hearts (n = 7) and significantly lower values in TAC hearts (n = 10) of 4.0 +/- 0.8 and 6.7 +/- 2.0 micromol/g wet wt for [ATP] (P < 0.04) and [PCr] (P < 0.001), respectively. The in vivo magnetic resonance [ATP] results are in good agreement with those obtained using an in vitro enzyme luminescent assay of perchloric acid extracts of the same hearts. In conclusion, a validated (31)P MRS method for quantifying [ATP] and [PCr] in the in vivo mouse heart using spatial localization and an external reference is described and used to demonstrate significant reductions in not only PCr/ATP but [ATP] in hypertrophied TAC hearts.

The mitochondrial protease AFG3L2 is essential for axonal development

The mitochondrial metalloprotease AFG3L2 assembles with the homologous protein paraplegin to form a supracomplex in charge of the essential protein quality control within mitochondria. Mutations of paraplegin cause a specific axonal degeneration of the upper motoneuron and, therefore, hereditary spastic paraplegia. Here we present two Afg3l2 murine models: a newly developed null and a spontaneous mutant that we found carrier of a missense mutation. Contrasting with the mild and late onset axonal degeneration of paraplegin-deficient mouse, Afg3l2 models display a marked impairment of axonal development with delayed myelination and poor axonal radial growth leading to lethality at P16. The increased severity of the Afg3l2 mutants is explained by two main molecular features that differentiate AFG3L2 from paraplegin: its higher neuronal expression and its versatile ability to support both hetero-oligomerization and homo-oligomerization. Our data assign to AFG3L2 a crucial role by linking mitochondrial metabolism and axonal development. Moreover, we propose AFG3L2 as an excellent candidate for motoneuron and cerebellar diseases with early onset unknown etiology.

Inhibition of UCP2 expression reverses diet-induced diabetes mellitus by effects on both insulin secretion and action

Recent characterization of the ability of uncoupling protein 2 (UCP2) to reduce ATP production and inhibit insulin secretion by pancreatic beta-cells has placed this mitochondrial protein as a candidate target for therapeutics in diabetes mellitus. In the present study we evaluate the effects of short-term treatment of two animal models of type 2 diabetes mellitus with an antisense oligonucleotide to UCP2. In both models, Swiss mice (made obese and diabetic by a hyperlipidic diet) and ob/ob mice, the treatment resulted in a significant improvement in the hyperglycemic syndrome. This effect was due not only to an improvement of insulin secretion, but also to improved peripheral insulin action. In isolated pancreatic islets, the partial inhibition of UCP2 increased ATP content, followed by increased glucose-stimulated insulin secretion. This was not accompanied by increased expression of enzymes involved in protection against oxidative stress. The evaluation of insulin action in peripheral tissues revealed that the inhibition of UCP2 expression significantly improved insulin signal transduction in adipose tissue. In conclusion, short-term inhibition of UCP2 expression ameliorates the hyperglycemic syndrome in two distinct animal models of obesity and diabetes. Metabolic improvement is due to a combined effect on insulin-producing pancreatic islets and in at least one peripheral tissue that acts as a target for insulin.

Molecularly imprinted solid-phase extraction combined with molecularly imprinted polymer-sensor: a diagnostic tool applicable to creatine deficiency syndrome

Primary creatine deficiency syndromes (CDS) are a new group of disorders caused by guanidinoacetate methyltransferase (GAMT) deficiency, which affects endogenous creatine biosynthesis with depletion of body creatine. A deficiency in creatine can be corrected by treatment with oral creatine supplementation and this necessitates a simple and sensitive screening method for early detection of creatine in dilute physiologic fluids. In this work an artificial receptor, molecularly imprinted polymer (MIP), for creatine was used both as a material for solid-phase extraction (SPE) and as a sensing element in a voltammetric sensor. Using the combination of molecularly imprinted solid-phase extraction (MISPE) with a complementary MIP sensor, the minimum detectable amount was found to be 0.0015 ng mL(-1) (RSD = 1.3%, S/N = 3). The MISPE-MIP sensor combination provided up to 60-fold preconcentration, which was more than sufficient for achieving the required quantification limit 50 ng mL(-1) (or 0.0025 ng mL(-1) after 2 x 10(4)-fold dilution) for creatine in human blood serum.

Regulation of insulin secretion and beta-cell mass by activating signal cointegrator 2

Activating signal cointegrator 2 (ASC-2) is a transcriptional coactivator of many nuclear receptors (NRs) and other transcription factors and contains two NR-interacting LXXLL motifs (NR boxes). In the pancreas, ASC-2 is expressed only in the endocrine cells of the islets of Langerhans, but not in the exocrine cells. Thus, we examined the potential role of ASC-2 in insulin secretion from pancreatic beta-cells. Overexpressed ASC-2 increased glucose-elicited insulin secretion, whereas insulin secretion was decreased in islets from ASC-2+/- mice. DN1 and DN2 are two dominant-negative fragments of ASC-2 that contain NR boxes 1 and 2, respectively, and block the interactions of cognate NRs with the endogenous ASC-2. Primary rat islets ectopically expressing DN1 or DN2 exhibited decreased insulin secretion. Furthermore, relative to the wild type, ASC-2+/- mice showed reduced islet mass and number, which correlated with increased apoptosis and decreased proliferation of ASC-2+/- islets. These results suggest that ASC-2 regulates insulin secretion and beta-cell survival and that the regulatory role of ASC-2 in insulin secretion appears to involve, at least in part, its interaction with NRs via its two NR boxes.

Determination of ATP as a fluorescence probe with europium(III)-doxycycline

A new spectrofluorimetric method has been developed for the determination of adenosine disodium triphosphate (ATP). We studied the interactions between the doxycycline (DC)-Eu3+ complex and adenosine disodium triphosphate (ATP) by using UV-visible absorption and fluorescence spectra. Using doxycycline (DC)-Eu3+ as a fluorescence probe, under the optimum conditions, ATP could remarkably enhance the fluorescence intensity of the DC-Eu3+ complex at lambda = 612 nm. The enhanced fluorescence intensity of the Eu3+ ion was in proportion to the concentration of ATP. The optimum conditions for the determination of ATP were also investigated. The linear ranges for ATP were 1.00 x 10(-7) - 2.00 x 10(-6) mol L(-1) with detection limits of 4.07 x 10(-8) mol L(-1). This method is simple, practical and relatively free of interference from coexisting substances, and can be successfully applied to the determination of ATP in samples. The mechanism of fluorescence enhancement between the doxycycline (DC)-Eu3+ complex and ATP was also studied.

The blood-brain barrier transmigrating single domain antibody: mechanisms of transport and antigenic epitopes in human brain endothelial cells

Antibodies against receptors that undergo transcytosis across the blood-brain barrier (BBB) have been used as vectors to target drugs or therapeutic peptides into the brain. We have recently discovered a novel single domain antibody, FC5, which transmigrates across human cerebral endothelial cells in vitro and the BBB in vivo. The purpose of this study was to characterize mechanisms of FC5 endocytosis and transcytosis across the BBB and its putative receptor on human brain endothelial cells. The transport of FC5 across human brain endothelial cells was polarized, charge independent and temperature dependent, suggesting a receptor-mediated process. FC5 taken up by human brain endothelial cells co-localized with clathrin but not with caveolin-1 by immunochemistry and was detected in clathrin-enriched subcellular fractions by western blot. The transendothelial migration of FC5 was reduced by inhibitors of clathrin-mediated endocytosis, K+ depletion and chlorpromazine, but was insensitive to caveolae inhibitors, filipin, nystatin or methyl-beta-cyclodextrin. Following internalization, FC5 was targeted to early endosomes, bypassed late endosomes/lysosomes and remained intact after transcytosis. The transcytosis process was inhibited by agents that affect actin cytoskeleton or intracellular signaling through PI3-kinase. Pretreatment of human brain endothelial cells with wheatgerm agglutinin, sialic acid, alpha(2,3)-neuraminidase or Maackia amurensis agglutinin that recognizes alpha(2,3)-, but not with Sambucus nigra agglutinin that recognizes alpha(2,6) sialylgalactosyl residues, significantly reduced FC5 transcytosis. FC5 failed to recognize brain endothelial cells-derived lipids, suggesting that it binds luminal alpha(2,3)-sialoglycoprotein receptor which triggers clathrin-mediated endocytosis. This putative receptor may be a new target for developing brain-targeting drug delivery vectors.

Examination of the requirement for ucp-4, a putative homolog of mammalian uncoupling proteins, for stress tolerance and longevity in C. elegans

Reactive oxygen species (ROS) are generated by mitochondrial respiration and can react with and damage cellular components. According to the free radical theory of aging, oxidative damage from mitochondrial ROS is a major cause of cellular decline during aging. Mitochondrial uncoupling proteins (UCPs) uncouple ATP production from electron transport and can be stimulated by free radicals, suggesting UCPs may perform a cytoprotective function. The nematode, Caenorhabditis elegans, contains one UCP-like protein, encoded by the ucp-4 gene. We have investigated the genetic requirement for ucp-4 in normal aging and stress resistance. Consistent with the hypothesis that ucp-4 encodes a putative uncoupling protein, animals lacking ucp-4 function contained elevated ATP levels. However, the absence of ucp-4 function did not affect adult lifespan or survival in the presence of thermal or oxidative stress. Together, these results demonstrate that ucp-4 is a negative regulator of ATP production in C. elegans, but is not required for normal lifespan.

A Yang-Invigorating Chinese Herbal Formula Enhances Mitochondrial Functional Ability and Antioxidant Capacity in Various Tissues of Male and Female Rats

The practice of traditional Chinese medicine (TCM) always emphasizes the prevention of diseases and delaying the onset of senility. In this regard, the maintenance of a balance of Yin and Yang-two opposing components involved in life activities as exemplified by the antagonistic action of the sympathetic and parasympathetic nervous systems-is essential in achieving a healthy condition. Previous studies have shown that long-term treatment with a Yang-invigorating Chinese herbal formula (VI-28) could increase red cell CuZn-superoxide dismutase (SOD) activity in male human subjects. In the present study, we examined the effects of chronic VI-28 treatment (80 and 240 mg/kg/day for 30 days) on red cell CuZn-SOD activity as well as mitochondrial functional ability and antioxidant components in various tissues of male and female rats. The results indicated that VI-28 treatment increased red cell CuZn-SOD activity as well as mitochondrial ATP generation capacity, reduced glutathione and alpha-tocopherol levels, and Mn-SOD activity in brain, heart, liver, and skeletal muscle tissues in both male and female rats to varying extents. The VI-28?induced increase in mitochondrial antioxidant capacity in various tissues was evidenced by the significant reduction in the extent of reactive oxygen species generation assessed by in vitro measurement. The red cell CuZn-SOD activities correlated positively with tissue mitochondrial antioxidant component levels/activity. The beneficial effect of VI-28 treatment on mitochondrial functional ability and antioxidant capacity may have clinical implications in the prevention of age-related diseases.

Determination of adenosine disodium triphosphate (ATP) using oxytetracycline-Eu3+ as a fluorescence probe by spectrofluorimetry

A new spectrofluorimetric method was developed for determination of adenosine disodium triphosphate (ATP). We studied the interactions between oxytetracycline (OTC)-Eu3+ complex and adenosine disodium triphosphate (ATP) by using UV-vis absorption and fluorescence spectra. Using oxytetracycline (OTC)-Eu3+ as a fluorescence probe, under the optimum conditions, ATP can remarkably enhance the fluorescence intensity of the OTC-Eu3+ complex at lambda = 612 nm and the enhanced fluorescence intensity of Eu3+ ion is in proportion to the concentration of ATP. Optimum conditions for the determination of ATP were also investigated. The linear ranges for ATP are 8.00 x 10(-8)-1.50 x 10(-6) mol L(-1) with detection limits of 2.67 x 10(-9) mol L(-1). This method is simple, practical and relatively free interference from coexisting substances and can be successfully applied to determination of ATP in samples. The mechanism of fluorescence enhancement between oxytetracycline (OTC)-Eu3+ complex and ATP was also studied.

Glucose or insulin, but not zinc ions, inhibit glucagon secretion from mouse pancreatic alpha-cells

The mechanisms by which hypoglycemia stimulates glucagon release are still poorly understood. In particular, the relative importance of direct metabolic coupling versus paracrine regulation by beta-cell secretory products is unresolved. Here, we compare the responses to glucose of 1) alpha-cells within the intact mouse islet, 2) dissociated alpha-cells, and 3) clonal alphaTC1-9 cells. Free cytosolic concentrations of ATP ([ATP](c)) or Ca(2+) ([Ca(2+)](c)) were imaged using alpha-cell-targeted firefly luciferase or a green fluorescent protein-based Ca(2+) probe ("pericam"), respectively. Consistent with a direct effect of glucose on alpha-cell oxidative metabolism, an increase in glucose concentration (from 0 or 3 mmol/l to 20 mmol/l) increased [ATP](c) by 7-9% in alpha-cells within the intact islet and by approximately 4% in alphaTC1-9 cells. Moreover, glucose also dose-dependently decreased the frequency of [Ca(2+)](c) oscillations in both dissociated alpha-cells and alphaTC1-9 cells. Although the effects of glucose were mimicked by exogenous insulin, they were preserved when insulin signaling was blocked with wortmannin. Addition of ZnCl(2) slightly increased the frequency of [Ca(2+)](c) oscillations but failed to affect glucagon release from either islets or alphaTC1-9 cells under most conditions. We conclude that glucose and insulin, but not Zn(2+) ions, independently suppress glucagon secretion in the mouse.

The effect of endogenous dopamine in rotenone-induced toxicity in PC12 cells

Deficiencies in Complex I have been observed in Parkinson's disease (PD) patients. Systemic exposure to rotenone, a Complex I inhibitor, has been shown to lead to selective dopaminergic cell death in vivo and toxicity in many in vitro models, including dopaminergic cell cultures. However, it remains unclear why rotenone seems to affect dopaminergic cells more adversely. Therefore, the role of dopamine (DA) in rotenone-induced PC12 cell toxicity was examined. Rotenone (1.0 muM) caused significant toxicity in differentiated PC12 cells, which was accompanied by decreases in ATP levels, changes in catechol levels, and increased DA oxidation. To determine whether endogenous DA makes PC12 cells more susceptible to rotenone, cells were treated with the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT) to reduce DA levels prior to rotenone exposure, and then cell viability was measured. No changes in rotenone-induced toxicity were observed with or without AMPT treatment. However, a potentiation of toxicity was observed following coexposure of PC12 cells to rotenone and methamphetamine. To determine whether this effect was due to DA, PC12 cells were depleted of DA prior to methamphetamine and rotenone cotreatment, resulting in a large attenuation in toxicity. These findings suggest that DA plays a role in rotenone-induced toxicity and possibly the vulnerability of DA neurons in PD.

Independent ATPase activity of Hsp90 subunits creates a flexible assembly platform

The ATPase activity of the molecular chaperone Hsp90 is essential for its function in the assembly of client proteins. To understand the mechanism of human Hsp90, we have carried out a detailed kinetic analysis of ATP binding, hydrolysis and product release. ATP binds rapidly in a two-step process involving the formation of a diffusion-collision complex followed by a conformational change. The rate-determining step was shown to be ATP hydrolysis and not subsequent ADP dissociation. There was no evidence from any of the biophysical measurements for cooperativity in either nucleotide binding or hydrolysis for the dimeric protein. A monomeric fragment, lacking the C-terminal dimerisation domain, showed no dependence on protein concentration and, therefore, subunit association for activity. The thermodynamic linkage between client protein binding and nucleotide affinity revealed ATP bound Hsp90 has a higher affinity for client proteins than the ADP bound form. The kinetics are consistent with independent Michaelis-Menten catalysis in each subunit of the Hsp90 dimer. We propose that Hsp90 functions in an open-ring configuration for client protein activation.

Relationship between the host cell mitochondria and the parasitophorous vacuole in cells infected with Encephalitozoon microsporidia

Encephalitozoon microsporidia proliferate and differentiate within a parasitophorous vacuole. Using the fluorescent probe, calcein, and the mitochondrial probe, MitoTracker-CMXRos, a vital method was developed that confirmed ultrastructural reports that the host cell mitochondria frequently lie in immediate proximity to the parasitophorous vacuole. Morphometry failed to demonstrate any infection-induced increase in host cell mitochondria as there was no correlation between the mitochondrial volume and the extent of infection as judged by the parasitophorous vacuole volume. The total ATP concentration of infected cells did not differ from that of uninfected cells in spite of the increased metabolic demands of the infection. Treatment with 10(-6) M albendazole, more than ten times the antiparasitic IC50 dose, and demecolcine had no subjective effect on the proximity of mitochondria to the parasitophorous vacuole membrane when studied by either transmission electron microscopy or by confocal microscopy even though these drug concentrations affected microtubule structure. Thus, once the association between mitochondria and the parasitophorous vacuole has been established, host cell microtubule integrity is probably not required for its maintenance. It is unlikely that the antimicrosporidial action of albendazole involves physically uncoupling developing parasite stages from host cell organelle metabolic support.

Axonal degeneration in paraplegin-deficient mice is associated with abnormal mitochondria and impairment of axonal transport

In several neurodegenerative diseases, axonal degeneration occurs before neuronal death and contributes significantly to patients' disability. Hereditary spastic paraplegia (HSP) is a genetically heterogeneous condition characterized by selective degeneration of axons of the corticospinal tracts and fasciculus gracilis. HSP may therefore be considered an exemplary disease to study the local programs mediating axonal degeneration. We have developed a mouse model for autosomal recessive HSP due to mutations in the SPG7 gene encoding the mitochondrial ATPase paraplegin. Paraplegin-deficient mice are affected by a distal axonopathy of spinal and peripheral axons, characterized by axonal swelling and degeneration. We found that mitochondrial morphological abnormalities occurred in synaptic terminals and in distal regions of axons long before the first signs of swelling and degeneration and correlated with onset of motor impairment during a rotarod test. Axonal swellings occur through massive accumulation of organelles and neurofilaments, suggesting impairment of anterograde axonal transport. Retrograde axonal transport is delayed in symptomatic mice. We speculate that local failure of mitochondrial function may affect axonal transport and cause axonal degeneration. Our data suggest that a timely therapeutic intervention may prevent the loss of axons.

Loss of m-AAA protease in mitochondria causes complex I deficiency and increased sensitivity to oxidative stress in hereditary spastic paraplegia

Mmutations in paraplegin, a putative mitochondrial metallopeptidase of the AAA family, cause an autosomal recessive form of hereditary spastic paraplegia (HSP). Here, we analyze the function of paraplegin at the cellular level and characterize the phenotypic defects of HSP patients' cells lacking this protein. We demonstrate that paraplegin coassembles with a homologous protein, AFG3L2, in the mitochondrial inner membrane. These two proteins form a high molecular mass complex, which we show to be aberrant in HSP fibroblasts. The loss of this complex causes a reduced complex I activity in mitochondria and an increased sensitivity to oxidant stress, which can both be rescued by exogenous expression of wild-type paraplegin. Furthermore, complementation studies in yeast demonstrate functional conservation of the human paraplegin–AFG3L2 complex with the yeast m-AAA protease and assign proteolytic activity to this structure. These results shed new light on the molecular pathogenesis of HSP and functionally link AFG3L2 to this neurodegenerative disease.

Validation of a simple liquid chromatography assay for creatine suitable for pharmacokinetic applications, determination of plasma protein binding and verification of percent labeled claim of various creatine products

Creatine has been quantified in various tissues by a range of methodologies. This paper reports on the development and validation of a simplified HPLC assay to determine plasma creatine, plasma protein binding of creatine, creatine in microdialysate and creatine in over-the-counter products. An isocratic, reversed-phase (C(18)) HPLC assay, using potassium phosphate monobasic (pH 4) as a mobile phase, was validated in human plasma and microdialysis perfusion fluid (normal saline). The lower limit of quantification for the assay was 1 mg l(-1) in saline and 5 mg l(-1) in plasma. The RSD was below 6% and accuracy was below 12% in both matrices. Protein binding in human plasma was found to be negligible (<10%). Over-the-counter creatine monohydrate products tested contained 100% creatine monohydrate. This assay was found to be suitable for pharmacokinetic studies and the assessment of plasma creatine and skeletal muscle microdialysate.

Suppression of beta cell energy metabolism and insulin release by PGC-1alpha

beta cell dysfunction is an important component of type 2 diabetes, but the molecular basis for this defect is poorly understood. The transcriptional coactivator PGC-1alpha mRNA and protein levels are significantly elevated in islets from multiple animal models of diabetes; adenovirus-mediated expression of PGC-1alpha to levels similar to those present in diabetic rodents produces a marked inhibition of glucose-stimulated insulin secretion from islets in culture and in live mice. This inhibition coincides with changes in metabolic gene expression associated with impaired beta cell function, including the induction of glucose-6-phosphatase and suppression of GLUT2, glucokinase, and glycerol-3-phosphate dehydrogenase. These changes result in blunting of the glucose-induced rise in cellular ATP levels and membrane electrical activity responsible for Ca(2+) influx and insulin exocytosis. These results strongly suggest that PGC-1alpha plays a key functional role in the beta cell and is involved in the pathogenesis of the diabetic phenotype.

Glutaric aciduria I: creatine supplementation restores creatinephosphate levels in mixed cortex cells from rat incubated with 3-hydroxyglutarate

The pathogenesis of neurological sequelae in glutaric aciduria I (GA I) is still unclear. Some evidence exists for compromised energy generation in the brain of patients with GA I resulting in 'slow-onset' excitotoxicity. Previously, we have shown a reduced activity of the mitochondrial ATPsynthase in cultured mixed cortex cells from neonatal rats incubated with 2-4mM 3-hydroxyglutarate (3-OH glut) for 24h. In the present study we measured cellular contents of high energy phosphate compounds (creatinephosphate CP, ATP, and ADP) in this model after a 24h incubation period with 2-4mM glutarate (glut) or 3-OH glut. 3-OH glut specifically led to a reduction of CP content in a dose-dependent manner, whereas concentrations of ATP, ADP, and AMP remained unchanged. The drop in CP-concentration could be prevented by preincubation with the non-competitive NMDA-receptor antagonist MK 801 or coincubation with 1mM creatine. NMDA-receptor associated ion channels may be opened due to a lack of energy inside the neurons caused by a reduction of CP. This is followed by membrane depolarization which could impair electrogenic creatine transport into the cell.