Enhanced glucose uptake via GLUT4 fuels recovery from calcium overload after ischaemia-reperfusion injury in sevoflurane- but not propofol-treated hearts

BACKGROUND

So far, no study has explored the effects of sevoflurane, propofol, and Intralipid on metabolic flux rates of fatty acid oxidation (FOX) and glucose oxidation (GOX) in hearts exposed to ischaemia-reperfusion.

METHODS

Isolated paced working rat hearts were exposed to 20 min of ischaemia and 30 min of reperfusion. Peri-ischaemic sevoflurane (2 vol%) and propofol (100 µM) in the formulation of 1% Diprivan(®) were assessed for their effects on oxidative energy metabolism and intracellular diastolic and systolic Ca(2+) concentrations. Substrate flux was measured using [(3)H]palmitate and [(14)C]glucose and [Ca(2+)] using indo-1AM. Western blotting was used to determine the expression of the sarcolemmal glucose transporter GLUT4 in lipid rafts. Biochemical analyses of nucleotides, ceramides, and 32 acylcarnitines were also performed.

RESULTS

Sevoflurane, but not propofol, improved the recovery of left ventricular work (P=0.008) and myocardial efficiency (P=0.008) compared with untreated ischaemic hearts. This functional improvement was accompanied by reduced increases in post-ischaemic diastolic and systolic intracellular Ca(2+) concentrations (P=0.008). Sevoflurane, but not propofol, increased GOX (P=0.009) and decreased FOX (P=0.019) in hearts exposed to ischaemia-reperfusion. GLUT4 expression was markedly increased in lipid rafts of sevoflurane-treated hearts (P=0.016). Increased GOX closely correlated with reduced Ca(2+) overload. Intralipid alone decreased energy charge and increased long-chain and hydroxyacylcarnitine tissue levels, whereas sevoflurane decreased toxic ceramide formation.

CONCLUSIONS

Enhanced glucose uptake via GLUT4 fuels recovery from Ca(2+) overload after ischaemia-reperfusion in sevoflurane- but not propofol-treated hearts. The use of a high propofol concentration (100 µM) did not result in similar protection.

Biochemical composition of the superficial layer of articular cartilage

To gain more information on the mechanism of lubrication in articular joints, the superficial layer of bovine articular cartilage was mechanically removed in a sheet of ice that formed on freezing the cartilage. Freeze-dried samples contained low concentrations of chondroitin sulphate and protein. Analysis of the protein by SDS PAGE showed that the composition of the sample was comparable to that of synovial fluid (SF). Attenuated total reflection infrared (ATR-IR) spectroscopy of the dried residue indicated that the sample contained mostly hyaluronan. Moreover, ATR-IR spectroscopy of the upper layer of the superficial layer, adsorbed onto silicon, showed the presence of phospholipids. A gel could be formed by mixing hyaluronan and phosphatidylcholine in water with mechanical properties similar to those of the superficial layer on cartilage. Much like the superficial layer of natural cartilage, the surface of this gel became hydrophobic on drying out. Thus, it is proposed that the superficial layer forms from hyaluronan and phospholipids, which associate by hydrophobic interactions between the alkyl chains of the phospholipids and the hydrophobic faces of the disaccharide units in hyaluronan. This layer is permeable to material from the SF and the cartilage, as shown by the presence of SF proteins and chondroitin sulphate. As the cartilage dries out after removal from the joint, the phospholipids migrate towards the surface of the superficial layer to reduce the surface tension. It is also proposed that the highly efficient lubrication in articular joints can, at least in part, be attributed to the ability of the superficial layer to adsorb and hold water on the cartilage surface, thus creating a highly viscous boundary protection.

Filter paper cards contaminated with EMLA cream produce artefacts on acylcarnitine analysis

Electrospray ionization tandem mass spectrometry is a widely applied method for the analysis of acylcarnitines in blood samples spotted on filter paper cards (Guthrie cards). When the filter paper cards are contaminated by EMLA cream, highly intense signals at m/z 221 and 235 are detected under ESI-MS/MS conditions, monitoring for precursors of m/z 85. These signals correspond to the active ingredients prilocaine and lidocaine in EMLA and overlap with the signals from the isotopically labelled internal standards (2H3)propionyl carnitine and (2H3)butyrylcarnitine. This interference prevents the proper quantification of the two short-chain acylcarnitines when samples are analysed without derivatization.

Hepatic carnitine palmitoyltransferase I deficiency: acylcarnitine profiles in blood spots are highly specific

BACKGROUND

In carnitine palmitoyltransferase I (CPT-I) deficiency (MIM 255120), free carnitine can be increased with no pathologic acylcarnitine species detectable. As inclusion of CPT-I deficiency in high-risk and newborn screening could prevent potentially life-threatening complications, we tested whether CPT-I deficiency might be diagnosed by electrospray ionization-tandem mass spectrometry (ESI-MS/MS).

METHODS

A 3.2-mm spot of whole blood dried on filter paper was extracted with 150 microL of methanol. After derivatization of carnitine and acylcarnitines to their butyl esters, the samples were analyzed by ESI-MS/MS with 37.5 pmol of L-[(2)H(3)]carnitine and 7.5 pmol of L-[(2)H(3)]palmitoylcarnitine as internal standards.

RESULTS

In all dried-blood specimens from each of three patients with CPT-I deficiency, we found an invariably increased ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)]. The ratio in patients was between 175 and 2000, or 5- to 60-fold higher than the ratio for the 99.9th centile of the normal newborn population in Bavaria (n = 177 842). No overlap with the values of children that were known to be supplemented with carnitine was detected [C0/(C16 + C18), 34 +/- 30; mean +/- SD; n = 27].

CONCLUSIONS

ESI-MS/MS provides a highly specific acylcarnitine profile from dried-blood samples. The ratio of free carnitine to the sum of palmitoylcarnitine and stearoylcarnitine [C0/(C16 + C18)] is highly specific for CPT-I deficiency and may allow presymptomatic diagnosis.

Brain S100A5 is a novel calcium-, zinc-, and copper ion-binding protein of the EF-hand superfamily

S100A5 is a novel member of the EF-hand superfamily of calcium-binding proteins that is poorly characterized at the protein level. Immunohistochemical analysis demonstrates that it is expressed in very restricted regions of the adult brain. Here we characterized the human recombinant S100A5, especially its interaction with Ca(2+), Zn(2+), and Cu(2+). Flow dialysis revealed that the homodimeric S100A5 binds four Ca(2+) ions with strong positive cooperativity and an affinity 20-100-fold higher than the other S100 proteins studied under identical conditions. S100A5 also binds two Zn(2+) ions and four Cu(2+) ions per dimer. Cu(2+) binding strongly impairs the binding of Ca(2+); however, none of these ions change the alpha-helical-rich secondary structure. After covalent labeling of an exposed thiol with 2-(4'-(iodoacetamide)anilino)-naphthalene-6-sulfonic acid, binding of Cu(2+), but not of Ca(2+) or Zn(2+), strongly decreased its fluorescence. In light of the three-dimensional structure of S100 proteins, our data suggest that in each subunit the single Zn(2+) site is located at the opposite side of the EF-hands. The two Cu(2+)-binding sites likely share ligands of the EF-hands. The potential role of S100A5 in copper homeostasis is discussed.

Mapping the zinc ligands of S100A2 by site-directed mutagenesis

S100 family proteins are characterized by short individual N and C termini and a conserved central part, harboring two Ca(2+)-binding EF-hands, one of them highly conserved among EF-hand family proteins and the other characteristic for S100 proteins. In addition to Ca(2+), several members of the S100 protein family, including S100A2, bind Zn(2+). Two regions in the amino acid sequences of S100 proteins, namely the helices of the N-terminal EF-hand motif and the very C-terminal loop are believed to be involved in Zn(2+)-binding due to the presence of histidine and/or cysteine residues. Human S100A2 contains four cysteine residues, each of them located at positions that may be important for Zn(2+) binding. We have now constructed and purified 10 cysteine-deficient mutants of human S100A2 by site-directed mutagenesis and investigated the contribution of the individual cysteine residues to Zn(2+) binding. Here we show that Cys(1(3)) (the number in parentheses indicating the position in the sequence of S100A2) is the crucial determinant for Zn(2+) binding in association with conformational changes as determined by internal tyrosine fluorescence. Solid phase Zn(2+) binding assays also revealed that the C-terminal residues Cys(3(87)) and Cys(4(94)) mediated a second type of Zn(2+) binding, not associated with detectable conformational changes in the molecule. Cys(2(22)), by contrast, which is located within the first EF hand motif affected neither Ca(2+) nor Zn(2+) binding, and a Cys "null" mutant was entirely incapable of ligating Zn(2+). These results provide new information about the mechanism and the site(s) of zinc binding in S100A2.

Evaluation of urinary acylglycines by electrospray tandem mass spectrometry in mitochondrial energy metabolism defects and organic acidurias

We analyzed the urinary acylglycine excretion in 26 patients with mitochondrial energy metabolism disorders and in 55 patients with organic acidurias by electrospray tandem mass spectrometry (ESI-MS/MS), monitoring precursor ions of m/z 90. Urinary concentrations of the different acylglycines were quantified using deuterated internal standards. Normal values for the most important acylglycines were established. In MCAD and MAD (neonatal form) deficiencies, typical excretion patterns of urinary acylglycines were found in all the samples. In isovaleric aciduria, propionic aciduria, and 3-methylcrotonylglycinuria typical glycine conjugates were always found. Methylmalonic aciduria (mutase deficiency), multiple carboxylase deficiency, and 3-hydroxy-3-methylglutaric aciduria revealed pathological acylglycine profiles, even if not specific for the disease. In all these diseases acylglycine excretion seems to be less influenced by the clinical status than organic acid excretion. This method is a useful diagnostic tool for these metabolic disorders, complementary to organic acids and acylcarnitine profiles.

Electrospray ionization mass spectrometry: analysis of the Ca2+-binding properties of human recombinant alpha-parvalbumin and nine mutant proteins

A set of 10 different recombinant human parvalbumins was used to establish a method for the investigation of the Ca2+-binding properties of proteins by electrospray ionization mass spectrometry (ESI-MS). Human PVWT was found to bind 2 mol Ca2+ ions/mol of protein, whereas its mutants (PVE101V, PVD90A, PVE62V, PVD51A, PVD90A,E101V, PVE62V,E101V, PVD51A,D90A, PVD51A,E62V, PVD51A,E62V, D90A,E101V) containing inactivating substitutions in the Ca2+-binding loops bind 0 or 1 Ca2+ ion per protein molecule, depending on the degree of inactivation. These findings fully agree with previously reported results obtained by flow dialysis experiments. The RP-HPLC desalted metal-free proteins were analyzed in 10 mM ammonium acetate at pH 7.0. The experimental conditions were optimized with the recombinant parvalbumin test system before analyzing the Ca2+-binding properties of rat and murine parvalbumins in muscle tissue extracts. ESI-MS revealed that (i) rat and murine alpha-parvalbumins each bind specifically two Ca2+ ions per protein molecule and (ii) both extracted parvalbumins were found to be posttranslationally modified; each protein is acetylated at the N-terminus. Finally, during our investigations of the murine parvalbumin a sequencing error was detected at the C-terminus where the amino acid at position 109 is Ser and not Thr as mentioned in the SwissProt data base (Accession No. P32848). This work demonstrates the great potential of the ESI-MS technique as a sensitive, specific, and rapid method for direct identification and determination of the stoichiometry of Ca2+-binding proteins and other metalloproteins.

Amino acid sequence determination of human S100A12 (P6, calgranulin C, CGRP, CAAF1) by tandem mass spectrometry

S100A12 has been isolated from human neutrophils. The molecular weight and the amino acid sequence of S100A12 was determined by electrospray-mass spectrometry, tandem mass spectrometry and Edman microsequence analysis. Interestingly, a sequence comparison of S100A12 with all known human S100 proteins revealed that S100A12 is the most divergent of the S100 proteins.