Paraoxonase, arylesterase and lactonase activities of paraoxonase-1 (PON1) in obese and severely obese women

Obesity is independently associated with disturbances in lipid and lipoprotein metabolism, oxidative stress, and is a well-established independent risk factor for cardiovascular diseases (CVD). Human paraoxonase 1 (PON1) is a pleotropic high-density lipoprotein (HDL)-associated enzyme with antioxidant and anti-inflammatory proprieties that have been suggested to contribute to the athero-protective function of the lipoprotein. The aim of this study was to investigate whether obesity is associated with PON1 activity and whether this association is influenced by oxidative stress, inflammation and HDL cholesterol (HDL-C) concentration. The promiscuous activities, arylesterase and paraoxonase, and the putative physiological activity, lactonase, of PON1 were assessed in the serum of 214 obese and severely obese, 101 overweight and 129 normal-weight women. Levels of high-sensitivity C-reactive protein (hs-CRP), hydroperoxides (by-products of lipid oxidative damage) and lipid profiles were also evaluated. Arylesterase activity was the only activity that significantly differed across the groups (ANOVA, p < .01), with the greatest decrease observed in individuals with body mass index (BMI) > 40 kg/m² compared to controls (p < .001). This activity was also inversely, although weakly (r = -0.160, p < .001) correlated with the BMI, and the association was independent of age and levels of oxidative stress and inflammation, but not of HDL-C concentration. In conclusion, our results suggest that the apparent obesity-associated decrement of PON1 activity might simply reflect the decrease in concentration of its plasmatic carrier.

Oxidative challenge in Alzheimer's disease: state of knowledge and future needs

A large body of experimental and postmortem findings indicate that Alzheimer's disease (AD) is associated with increased oxidative stress (OxS) levels in the brain. Despite the current limitations of OxS assessment in living subjects, recent data suggest that oxidative challenge might increase early both in the central nervous system and peripheral fluids. The aim of this review was to provide an overview of the existing literature linking systemic OxS to brain OxS in AD. We firmly believe that continued research aimed at overcoming the methodological and design issues affecting the body of studies in this field is mandatory for successful development of an effective antioxidant-based treatment of AD.

Changes in protein expression in two cholangiocarcinoma cell lines undergoing formation of multicellular tumor spheroids in vitro

Epithelial-to-Mesenchymal Transition (EMT) is relevant in malignant growth and frequently correlates with worsening disease progression due to its implications in metastases and resistance to therapeutic interventions. Although EMT is known to occur in several types of solid tumors, the information concerning tumors arising from the epithelia of the bile tract is still limited. In order to approach the problem of EMT in cholangiocarcinoma, we decided to investigate the changes in protein expression occurring in two cell lines under conditions leading to growth as adherent monolayers or to formation of multicellular tumor spheroids (MCTS), which are considered culture models that better mimic the growth characteristics of in-vivo solid tumors. In our system, changes in phenotypes occur with only a decrease in transmembrane E-cadherin and vimentin expression, minor changes in the transglutaminase protein/activity but with significant differences in the proteome profiles, with declining and increasing expression in 6 and in 16 proteins identified by mass spectrometry. The arising protein patterns were analyzed based on canonical pathways and network analysis. These results suggest that significant metabolic rearrangements occur during the conversion of cholangiocarcinomas cells to the MCTS phenotype, which most likely affect the carbohydrate metabolism, protein folding, cytoskeletal activity, and tissue sensitivity to oxygen.

Serum ferroxidase activity in patients with multiple sclerosis: a pilot study

Emerging evidence suggests that oxidative stress might contribute to demyelination and axonal damage in multiple sclerosis (MS). Ferroxidase (FeOx) activity of ceruloplasmin prevents the formation of free radicals from Fe(2+) by promoting the incorporation of this pro-oxidant ion to transferrin. The aim of our study was to investigate serum FeOx activity in a cohort of patients with MS and neurological controls. Serum FeOx activity was determined in 69 relapsing-remitting patients with MS and in 62 patients with other inflammatory neurological disorders (OIND) and 52 patients with other non-inflammatory neurological disorders (NIND) as controls. Serum FeOx activity was lower (p<0.01) in MS and OIND than in NIND, without any significant differences among MS patients grouped according to clinical and magnetic resonance evidence of disease activity. A reduced serum FeOx activity, which can potentially lead to a rise in oxidative stress-induced biomolecular damage, seems to be a shared condition in inflammatory disorders of the central nervous system including MS.

Accumulation of central fat correlates with an adverse oxidative balance in non-obese postmenopausal women

The aim of the present study was to investigate whether accumulation of central fat is correlated with systemic oxidative stress (OxS) in non-obese apparently healthy postmenopausal women. Serum parameters of OxS (hydroperoxides and non-enzymatic antioxidants) along with body fat distribution, as assessed by dual-energy-X-ray absorptiometry (DXA), were evaluated in 134 non-obese postmenopausal women. Multiple regression analysis showed that central (trunk) fat significantly correlated with both markers of OxS independently of confounding factors (i.e. BMI, smoking, age, hypertension, legs and arms fat mass). In specific, the standardized regression coefficient was positive for hydroperoxides (β = 0.324, p < 0.05) and negative for antioxidants (β = -0.495, p < 0.01) level. In conclusion, the current data showed that the increase in central fat is an independent predictor of OxS condition among non-obese women in postmenopausal status. The possible pro-oxidant effects of the excess in central adiposity might be more harmful among post- than among pre-menopausal women, due to the postulated ability of E2 to contrast oxidative challenge and the related diseases.

Comparative proteomic analysis of ductal breast carcinoma demonstrates an altered expression of chaperonins and cytoskeletal proteins

The aim of the present study was to analyze the protein composition of ductal breast carcinoma and the surrounding normal tissue in individual patients using comparative 2D proteomics and mass spectrometry to detect candidate disease biomarkers for diagnosis and prognosis. Samples of normal and cancerous tissue obtained form 28 patients were analyzed. Chaperonins and cytoskeletal proteins predominated among the 11 proteins for which major changes in abundance were detected. Of these 11 proteins with an altered expression, 2 had a decreased expression and 9 had an increased expression. In addition, the abundance of a few cytokeratins was also altered; however, they were not capable of serving as specific circulatory biomarkers. The proteins which we observed to exhibit an altered expression in infiltrating ductal breast carcinoma may be exploited as novel targets for therapeutic interventions or represent novel diagnostic/prognostic markers for the early detection of aggressive tumors, particularly those with multridrug-resistant phenotypes during the earlier stages of the disease.

Effects of the regulatory ligands calcium and GTP on the thermal stability of tissue transglutaminase

Tissue transglutaminase undergoes thermal inactivation with first-order kinetics at moderate temperatures, in a process which is affected in opposite way by the regulatory ligands calcium and GTP, which stabilize different conformations. We have explored the processes of inactivation and of unfolding of transglutaminase and the effects of ligands thereon, combining approaches of differential scanning calorimetry (DSC) and of thermal analysis coupled to fluorescence spectroscopy and small angle scattering. At low temperature (38-45°C), calcium promotes and GTP protects from inactivation, which occurs without detectable disruption of the protein structure but only local perturbations at the active site. Only at higher temperatures (52-56°C), the protein structure undergoes major rearrangements with alterations in the interactions between the N- and C-terminal domain pairs. Experiments by DSC and fluorescence spectroscopy clearly indicate reinforced and weakened interactions of the domains in the presence of GTP and of calcium, and different patterns of unfolding. Small angle scattering experiments confirm different pathways of unfolding, with attainment of limiting values of gyration radius of 52, 60 and 90 Å in the absence of ligands and in the presence of GTP and calcium. Data by X-rays scattering indicate that ligands influence retention of a relatively compact structure in the protein even after denaturation at 70°C. These results suggest that the complex regulation of the enzyme by ligands involves both short- and long-range effects which might be relevant for understanding the turnover of the protein in vivo.

Thermodynamics of binding of regulatory ligands to tissue transglutaminase

The transamidating activity of tissue transglutaminase is regulated by the ligands calcium and GTP, via conformational changes which facilitate or interfere with interaction with the peptidyl-glutamine substrate. We have analysed binding of these ligands by calorimetric and computational approaches. In the case of GTP we have detected a single high affinity site (K (D) approximately 1 microM), with moderate thermal effects suggestive that binding GTP involves replacement of GDP, normally bound to the protein. On line with this possibility no significant binding was observed during titration with GDP and computational studies support this view. Titration with calcium at a high cation molar excess yielded a complex binding isotherm with a number of "apparent binding sites" in large excess over those detectable by equilibrium dialysis (6 sites). This binding pattern is ascribed to occurrence of additional thermal contributions, beyond those of binding, due to the occurrence of conformational changes and to catalysis itself (with protein self-crosslinking). In contrast only one site for binding calcium with high affinity (K (D) approximately 0.15 microM) is observed with samples of enzyme inactivated by alkylation at the active site (to prevent enzyme crosslinkage and thermal effects of catalysis). These results indicate an intrinsic ability of tissue transglutaminase to bind calcium with high affinity and the necessity of careful reassessment of the enzyme regulatory pattern in relation to the concentrations of ligands in living cells, taking also in account effects of ligands on protein subcellular compartimentation.

Interaction with heparin protects tissue transglutaminase against inactivation by heating and by proteolysis

The considerable affinity of tissue transglutaminase for heparin was the basis for use of heparin-based affinity matrices for enzyme purification. Interaction of transglutaminase with heparin might mimic the physiological binding to membrane heparan sulfates, accounting for the limited but significant fraction of enzyme exposed at cell surface to crosslink ECM proteins. Exploring effects of heparin on transglutaminase activity and stability, we have noted that heparin only slightly affects activity in vitro, but the protein against heat treatment and proteolysis.

Characterization of cholylglycine hydrolase from a bile-adapted strain of Xanthomonas maltophilia and its application for quantitative hydrolysis of conjugated bile salts

Purified bile salt hydrolase from bile-adapted Xanthomonas maltophilia displays Michaelis-Menten kinetics on cholylglycine and cholyltaurine and hydrolyzes bile salts also in crude bovine bile. The protein is a dimer and is resistant to proteinases and to heating at 55 to 60 degrees C for up to 60 min, in agreement with calorimetric data.