Giuliana Merati

Gene Polymorphisms Predicting High Plasma Levels of Coagulation and Fibrinolysis Proteins: A Study in Centenarians

Gene polymorphisms associated with the plasma levels of fibrinogen, factor VII, and plasminogen activator inhibitor 1 (PAI-1)-hemostasis proteins that help to predict the risk of atherothrombotic disease-were compared in 124 healthy individuals > or = 100 years old and 130 young, healthy individuals to identify genetic influences on extreme longevity. We investigated the restriction fragment length polymorphism G/A-455 located in the promoter of the beta-fibrinogen gene, the guanine insertion/deletion polymorphism 4G/5G in the promoter of the PAI-1 gene, and the R353Q substitution polymorphism in exon 8 of the factor VII gene. Alleles and genotypes associated with elevated plasma levels of fibrinogen and factor VII were found with similar frequencies in centenarians and in the comparison group. However, in centenarians there was a significantly higher frequency of the 4G allele and of the homozygous 4G4G genotype associated with high PAI-1 levels. Since high PAI-1 is considered a predictor of recurrent myocardial infarction in young men, it is intriguing that the corresponding genetic marker is more frequent in centenarians who have escaped major age-related atherothrombotic disease and reached the extreme limits of human life. Homozygosity for the 4G allele, despite its association with impaired fibrinolysis, is compatible with successful aging.

Role of Chloride Ions in Modulation of the Interaction between von Willebrand Factor and ADAMTS-13

The degradation of von Willebrand factor (VWF) depends on the activity of a zinc protease (referred to as ADAMTS-13), which cleaves VWF at the Tyr1605-Met1606 peptide bond. Little information is available on the physiological mechanisms involved in regulation of AD-AMTS-13 activity. In this study, the role of ions on the ADAMTS-13/VWF interaction was investigated. In the presence of 1.5 m urea, the protease cleaved multimeric VWF in the absence of NaCl at pH 8.00 and 37 °C, with an apparent kcat/Km ≅ 3.4 × 104 m-1 s-1, but this value decreased by ∼10-fold in the presence of 0.15 m NaCl. Using several monovalent salts, the inhibitory effect was attributed mostly to anions, whose potency was inversely related to the corresponding Jones-Dole viscosity B coefficients (\batchmode \documentclass[fleqn,10pt,legalpaper]{article} \usepackage{amssymb} \usepackage{amsfonts} \usepackage{amsmath} \pagestyle{empty} \begin{document} \(\mathrm{ClO}_{4}^{-}{>}\mathrm{Cl}^{-}{>}\mathrm{F}^{-}\) \end{document}). The specific inhibitory effect of anions was due to their binding to VWF, which caused a conformational change responsible for quenching the intrinsic fluorescence of the protein and reducing tyrosine exposition to bulk solvent. Ristocetin binding to VWF could reduce the apparent affinity and reverse the inhibitory effect of chloride. We hypothesize that, after secretion into the extracellular compartment, VWF is bound by chloride ions abundantly present in this milieu, becoming unavailable to proteolysis by AD-AMTS-13. Shear forces, which facilitate GpIbα binding (this effect being artificially obtained by ristocetin), can reverse the inhibitory effect of chloride, whose concentration gradient across the cell membrane may represent a simple but efficient strategy to regulate the enzymatic activity of ADAMTS-13.

Chemical cross-linking of ferredoxin to spinach thylakoids: Evidence for two independent binding sites of ferredoxin to the membrane☆

Ferredoxin has been chemically cross‐linked to thylakoids by using N‐ethyl‐3‐(3‐dimethylaminopropyl)‐carbodiimide. The membranes thus treated became able to photoreduce cytochrome c and to catalyze the NADPH‐cytochrome c reductase reaction without adding exogenous ferredoxin. Preincubation of thylakoids with an antibody against ferredoxin‐NADP+ reductase before carbodiimide treatment or removal of the reductase by mild trypsin treatment after the cross‐linking reaction did not alter the cytochrome c photoreduction activity of the treated membranes. Two independent binding sites of ferredoxin to thylakoids are thus inferred: one site is shown to be the membrane‐bound reductase, the second is suggested to be at the level of the photosystem I complex.

Antioxidant Activity of Ubiquinone-3 in Human Low Density Lipoprotein

The ability of ubiquinone-3, a short chain ubiquinone homologue, to prevent Cu2+ induced oxidation of human low density lipoprotein was investigated. The results are as follows: in the presence of ubiquinone-3 the extent of peroxidation, as determined by the formation of thiobarbituric acid reactive substances, was only one third of that found in its absence; the quinone can also prevent the fragmentation of apolipoprotein B-100 and the increase of the net negative surface charge of the particle.

Determination of Lp(a) and APO(a) in an Italian population

SummaryPlasma lipoprotein(a) [Lp(a)] levels were determined in an Italian population subdivided according to age and sex. The distribution of plasma Lp(a) levels was highly skewed, with 75% of the subjects having less than 10 mg/dl. No significant differences were found in the plasma Lp(a) levels of the two age groups, but women had significandy higher levels than men. There was no significant correlation between Lp(a) levels and the other lipid and lipoprotein parameters studied, with the exception of a weak correlation between Lp(a) levels and both total cholesterol and low density lipoprotein-cholesterol in younger women. Apoprotein(a) phenotyping was performed in about one-third of the population; an inverse relationship between the molecular weight of the different isoforms and plasma concentrations of Lp(a) was observed.