CKD Increases Carbonylation of HDL and Is Associated with Impaired Antiaggregant Properties

BACKGROUND

CKD is associated with increased oxidative stress that correlates with occurrence of cardiovascular events. Modifications induced by increased oxidative stress particularly affect circulating lipoproteins such as HDL that exhibit antiatheromatous and antithrombotic properties in vitro.

METHODS

To explore the specific role of oxidative modifications of HDL in CKD and their effect on the platelet-targeting antiaggregant properties of HDL, we used a CKD (5/6 nephrectomy) rabbit model. For ex vivo assessment of the antiaggregant properties of HDL, we collected blood samples from 15 healthy volunteers, 25 patients on hemodialysis, and 20 on peritoneal dialysis. We analyzed malondialdehyde, 4-hydroxynonenal (HNE), and 4-hydroxy-2-hexenal protein adduct levels. Platelet aggregation and activation were assessed by aggregometry, thromboxane B2 assay, or FACS. We modified HDL from controls by incubating it overnight at 37°C with 100 µM of HNE.

RESULTS

HDL from CKD rabbits and patients on hemodialysis had HNE adducts. The percentage of platelet aggregation or activation induced by collagen was significantly higher when platelets were incubated with HDL from CKD rabbit and hemodialysis groups than with HDL from the control group. In both rabbits and humans, platelet aggregation and activation were significantly higher in the presence of HNE-modified HDL than with HDL from their respective controls. Incubation of platelets with a blocking antibody directed against CD36 or with a pharmacologic inhibitor of SRC kinases restored the antiaggregative phenotype in the presence of HDL from CKD rabbits, patients on hemodialysis and peritoneal dialysis, and HNE-modified HDL.

CONCLUSIONS

HDL from CKD rabbits and patients on hemodialysis exhibited an impaired ability to inhibit platelet aggregation, suggesting that altered HDL properties may contribute to the increased cardiovascular risk in this population.

Production and crystallization of the C-propeptide trimer from human procollagen III

The C-propeptide domains of the fibrillar procollagens, which are present throughout the Metazoa in the form of ∼90 kDa trimers, play crucial roles in both intracellular molecular assembly and extracellular formation of collagen fibrils. The first crystallization of a C-propeptide domain, that from human procollagen III, is described. Following transient expression in mammalian 293T cells of both the native protein and a selenomethionine derivative, two crystal forms of the homotrimer were obtained: an orthorhombic form (P2(1)2(1)2(1)) that diffracted to 1.7 Å resolution and a trigonal form (P321) that diffracted to 3.5 Å resolution. Characterization by MALDI-TOF mass spectrometry allowed the efficiency of selenomethionine incorporation to be determined.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and nuclear magnetic resonance analyses of end-functionalized saccharidic polymers: an example of a useful analytical technique combination

The living cationic polymerization of a saccharidic monomer (1,2:3,4-di-O-isopropylidene-6-O-(2-vinyloxyethyl)-D-galactopyranose, GVE) gives rise to aldehyde end-capped polymers (PGVE--CHO) of low molar masses (<10 000 Da) and low molar mass distribution (<1.2). These polymers were derivatized by selective introduction of either hexamethylenediamine (PGVE-NH2) or 9-fluorenylmethyl carbazate (PGVE-Fmoc) end groups. The resulting polymers were fully characterized by complementary use of nuclear magnetic resonance (1H NMR) and matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS). The expected structure according to the polymerization mechanism, the occurrence of side reactions and the success of the post-functionalization reactions were confirmed.

Photoaffinity labeling of human sex hormone-binding globulin using 17alpha-alkylamine derivatives of 3beta-androstanediol substituted with azidonitrophenylamido, azidonitrophenylamino, or trifluoroazidonitrophenylamino chromophores. Localization of Trp-84 in the vicinity of the steroid-binding site

Purified human SHBG was photoaffinity labeled with 17alpha-aminomethyl (M), 17alpha-aminoethyl (E), and 17alpha-aminopropyl (P) derivatives of [3alpha-(3)H]-5alpha-androstane-3beta,17beta-diol coupled to 5-azido-2-nitrobenzoylamido (ANB), 4-azido-2-nitrophenylamino (ANP), and 5-azido-2-nitro-3,4,6-trifluorophenylamino (ANTFP) chromophores. Successful labeling was achieved in all cases except for the two photoreagents with the shortest side chains, namely, ANP-M and ANTFP-M derivatives. Edman sequencing and mass spectrometry of immunopurified photolabeled tryptic fragments revealed that radioactivity was present either on the sequence of residues 73-94, uniquely at the level of Trp-84 (stable covalent labeling), or on one of the two overlapping sequences of residues 126-134 and 126-135, at the level of Pro-130 (labile labeling) and Lys-134 (either stable or partially labile labeling), respectively. The same Trp-84 was photolabeled with the three ANB derivatives of increasing lengths, and by the ANP-P photoreagent. This residue was the exclusive target for the shortest [(3)H]ANB-M photoreagent but was a minor site for the longest [(3)H]ANB-P photoreagent, essentially recovered at the level of Pro-130. The [(3)H]ANB-E photoreagent of intermediate size also labeled exclusively Trp-84, except in some experiments in which photolabeling was recovered predominantly at the level of Pro-130. The [(3)H]ANP-P photoreagent with an overall length similar to that of the ANB-P photoreagent labeled simultaneously Trp-84 (minor site) and Lys-134. The other [(3)H]ANP-E, [(3)H]ANTFP-E, and [(3)H]ANTFP-P derivatives labeled in all cases Lys-134. These findings indicate that the conserved Trp-84 and the two Pro-130 and Lys-134 residues are all located in the vicinity of the D ring of steroid ligands and remain freely accessible from the C17alpha position, thus providing biochemical data delineating the corresponding region of the steroid-binding site.

Specific photoaffinity-labeling of Tyr-50 on the heavy chain and of Tyr-32 on the light chain in the steroid combining site of a mouse monoclonal anti-estradiol antibody using C3-, C6-, and C7-linked 5-azido-2-nitrobenzoylamidoestradiol photoreagents

A mouse monoclonal anti-7-(O-carboxymethyl)oximinoestradiol antibody 9D3, raised against the same immunogen as that employed for generating the reported anti-estradiol antibody 15H11 [Rousselot, P., et al. (1997) Biochemistry 36, 7860-7868], was found to exhibit an opposite specificity profile with a much stronger recognition of the D-ring than of the A-ring extremity of the steroid, but a similar lack of specificity for both 6- and 7-positions of the B-ring. This antibody was photoaffinity-labeled with five (5-azido-2-nitrobenzoyl)amido (ANBA) derivatives of [17alpha-(3)H]estradiol, synthesized from 3-aminoethyloxy, 3-(aminoethylamido)carboxymethyloxy, 6alpha- and 6beta-amino, and 7-[O-(aminoethylamido)carboxymethyl]oximino precursors. After tryptic digestion, the radioactive peptides on L and H chains were immunopurified with the immobilized antibody 9D3, separated by reversed-phase liquid chromatography, sequenced, and characterized by mass spectrometry, including post-source decay-matrix-assisted laser desorption/ionization time-of-flight mass spectrometry. The long 3-(ANBA-ethylamido)carboxymethyl ether photoreagent was found to label TyrL-32 (on CDR L1), whereas no labeling was observed with the shorter 3-derivative, a result in agreement with a binding pocket large enough to explain the high cross-reactivity with estradiol 3-conjugates. The two 6alpha- and 6beta-ANBA-estradiol isomers, as well as the 7-[O-(ANBA-ethylamido)carboxymethyl]oximinoestradiol photoreagent derived from the steroid hapten, labeled the same TyrL-32 residue. The 6beta-ANBA epimer also labeled TyrH-50 (at the basis of CDR H2). These experiments indicate that TyrL-32 is freely accessible from the three C3, C6, and C7 positions, all presumed to be exposed to solvent, while TyrH-50 is probably located on the beta-face of estradiol. These results, obtained in solution, provide experimental data useful for molecular modeling of the steroid-antibody complex.

Hydrolysis of glycine-containing elastin pentapeptides by LasA, a metalloelastase from Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen that causes severe infections in vulnerable hosts. It may produce various virulence factors including proteases. Among them, LasA possesses both elastolytic and staphylolytic (hydrolysis of pentaglycine cross-links in the cell wall peptidoglycan) activities. To understand if its elastolytic activity results from a preference for glycine-rich substrates, we studied its ability to hydrolyse the 65 pentapeptides of human tropoelastin containing at least three glycines. As demonstrated by capillary electrophoresis (CE), 22 of these peptides were hydrolysed by LasA, generally at a single peptide bond and the catalytic ratio kcat/KM was determined for most of them. The highest value was obtained for LGGGA, 59 +/- 9 min(-1) x mmol(-1) x L. The specificity of hydrolysis was elucidated by CE, liquid secondary ion mass spectrometry and, in some cases, collision activated dissociation-mass analysis of ion kinetic energy. The preferred cleavage sites are GG and GA peptide bonds, the sequence GG(cleavage site)A being especially sensitive to hydrolysis. Both positions P2 and P'2 must be occupied for hydrolysis and the presence of an amino acid in P3 (but not in P'3) significantly increases the catalytic ratio. Considering these results, about 30 GGX sequences (X: G, A or Y) of human tropoelastin could be susceptible to LasA elastolysis.

Protective role of platelets in chronic (Balb/C) and acute (CBA/J) Plasmodium berghei murine malaria

The role of blood platelets in the pathogenesis of malaria remains unclear. In this study we investigated the role of experimentally caused thrombocytopaenia in chronic (Balb/C) and acute (CBA/J) Plasmodium-berghei-induced murine malaria. A group of 30 Balb/C mice were rendered thrombocytopaenic by injection of anti-mouse platelet serum given every 2 days from day 2 to day 8 after malaria infection. Compared with the control group, thrombocytopaenic mice showed a greater mortality. The Kaplan-Meier estimate of the risk of death was 4.37-fold higher in the thrombocytopaenic group. Parasitaemia and weight loss was in agreement with the protective effect of platelets. In the acute malaria model, the survival rate was less significant but the estimated risk of death was 1.7-fold higher in the treated group. These results suggesting a protective role of platelets in murine malaria are not in line with previous reports of the literature. Taken together our data suggest, however, that platelets, similarly to some inflammatory cytokines like TNF, play a dual role in the pathogenesis of malaria. Depending on experimental conditions, e.g. the time of onset of thrombocytopaenia, the beneficial role of platelets may outweigh the deleterious one.

[Study of plasma acylcarnitines using tandem mass spectrometry. Application to the diagnosis of metabolism hereditary diseases]

BACKGROUND

L-carnitine is known to transport long chain fatty acids through the mitochondrial membrane but also to export accumulated acyl-CoA's as acylcarnitine esters. Acylcarnitine identification in body fluids allows the diagnosis of mitochondrial inborn errors especially fatty oxidation defects. Tandem mass spectrometry represents a new method for isolation and identification of acylcarnitines in plasma or in blood spotted onto filter paper (Guthrie cards).

MATERIAL AND METHODS

In order to validate our method, we studied 30 plasmas from children affected with 15 different inborn errors of metabolism and five amniotic fluids from fetuses affected with several organic acidurias. Fourty-six samples from children at risk for mitochondrial fatty oxidation disorders have been analyzed. We developed a method of tandem mass spectrometry with liquid secondary ion mass spectrometry using deuterated acylcarnitines as internal standards.

RESULTS

This method is very sensitive (detection limit = 2 microM). In all affected patients specific acylcarnitine signals corresponding to the metabolic block were constantly found. This confirms the diagnosis and validates the method. Among the 46 at risk children, four defects of long chain fatty acid oxidation were identified.

CONCLUSION

This new method is of great interest especially for the long chain fatty acid oxidation defects. These defects are very difficult to diagnose with classical methods as urinary organic acid profiling. A small amount of plasma (100 microL) or blood spotted onto paper is required. The acylcarnitine profile allows a rapid diagnosis if a dedicated apparatus is available.