Mass spectrometric determination of early and advanced glycation in biology

Protein glycation in biological systems occurs predominantly on lysine, arginine and N-terminal residues of proteins. Major quantitative glycation adducts are found at mean extents of modification of 1–5 mol percent of proteins. These are glucose-derived fructosamine on lysine and N-terminal residues of proteins, methylglyoxal-derived hydroimidazolone on arginine residues and N^ε-carboxymethyl-lysine residues mainly formed by the oxidative degradation of fructosamine. Total glycation adducts of different types are quantified by stable isotopic dilution analysis liquid chromatography-tandem mass spectrometry (LC-MS/MS) in multiple reaction monitoring mode. Metabolism of glycated proteins is followed by LC-MS/MS of glycation free adducts as minor components of the amino acid metabolome. Glycated proteins and sites of modification within them – amino acid residues modified by the glycating agent moiety - are identified and quantified by label-free and stable isotope labelling with amino acids in cell culture (SILAC) high resolution mass spectrometry. Sites of glycation by glucose and methylglyoxal in selected proteins are listed. Key issues in applying proteomics techniques to analysis of glycated proteins are: (i) avoiding compromise of analysis by formation, loss and relocation of glycation adducts in pre-analytic processing; (ii) specificity of immunoaffinity enrichment procedures, (iii) maximizing protein sequence coverage in mass spectrometric analysis for detection of glycation sites, and (iv) development of bioinformatics tools for prediction of protein glycation sites. Protein glycation studies have important applications in biology, ageing and translational medicine – particularly on studies of obesity, diabetes, cardiovascular disease, renal failure, neurological disorders and cancer. Mass spectrometric analysis of glycated proteins has yet to find widespread use clinically. Future use in health screening, disease diagnosis and therapeutic monitoring, and drug and functional food development is expected. A protocol for high resolution mass spectrometry proteomics of glycated proteins is given.     

Synthesis,Crystal Structure and Thermal Decomposition of the New Cadmium Selenite Chloride,Cd4(SeO3)2OCl2

A synthetic study in the Cd-Se-O-Cl system led to formation of the new oxochloride compound Cd₄(SeO₃)₂OCl₂ via solid state reactions. The compound crystallizes in the orthorhombic space group Fmmm with cell parameters a = 7.3610(3) Å, b = 15.4936(2) Å, c = 17.5603(3) Å, Z = 8, S = 0.969, F(000) = 2800, R = 0.0185, R_w = 0.0384. Single crystal X-ray data were collected at 293 K. The crystal structure can be considered as layered and the building units are distorted [Cd(1)O₆] octahedra, distorted [Cd(2)O₈] cubes, irregular [Cd(3)O₄Cl₂] polyhedra and SeO₃E trigonal pyramids. There are two crystallographically unique Cl atoms that both are half occupied. Thermogravimetric studies show that the compound starts to decompose at 500°C. The crystal structure of the new compound is closely related to the previously described compound Cd₄(SeO₃)₂Cl₄(H₂O).     

Post-pollination biochemical changes in the floral organs of<Emphasis Type="Italic">Rhynchostylis retusa</Emphasis> (L.) Bl. and<Emphasis Type="Italic">Aerides multiflora</Emphasis> Roxb. (Orchidaceae)

If left unpollinated, the flowers ofAerides multiflora (Roxb.) andRhynchostylis retusa (L.) Bl. can remain fresh for 17 and 24 d, respectively. However, they begin to wilt at 2 to 3 days after pollination (DAP) and 3 to 4 DAP, respectively, and become senescent at 5 DAP and 7 DAP, respectively. When measured at two developmental phases — Stage 1, start of wilting and Stage 2, progression to senescence — all the floral organs from pollinated flowers had higher contents of total soluble sugars, reducing sugars, and free amino acids than those from unpollinated flowers. A corresponding increase was noted in the activities of hydrolytic enzymes, i.e., α-amylase, β-amylase, and invertase, and proteolytic enzymes (proteases) in those organs. This indicated that signals related to pollination had up-regulated those activities, leading to a breakdown of complex molecules into simpler ones for mobilization. The amounts of sugars and enzyme activity were relatively greater in the pollinated flowers ofA. multiflora compared withR. retusa, and levels were always higher in the floral lips and perianths. When inhibitors of auxin (0.25 mM TIBA) or ethylene (0.25 mM AgNO₂) were applied to the pollinated flowers, their senescence was partially prevented, thus signifying hormonal involvement in governing the pollination-induced biochemical alterations normally found in those organs.     

Induction of prolonged asthma tolerance by IL-10-differentiated dendritic cells: differential impact on airway hyperresponsiveness and the Th2 immunoinflammatory response

IL-10-differentiated dendritic cells (DC10s) can prevent allergen sensitization and reverse the asthma phenotype in mice with established disease. However, little is known about the time-frames over which this tolerance is effective. We report that at 2 wk after i.p. or transtracheal delivery of 1 × 10(6) OVA-, but not house dust mite- presenting, DC10s to OVA-asthmatic mice, significant diminution of airway hyperresponsiveness (AHR) was first apparent, whereas AHR was abrogated between 3 and 10 wk posttreatment. At 13 wk, AHR returned to pretreatment levels but could again be reversed by DC10 retreatment. The impact of a single DC10 treatment on airway eosinophil and Th2 cytokine responses to recall OVA challenge, and on OVA-specific IgE/IgG1 responses, was substantial at 3 wk posttreatment, but progressively increased thereafter, such that at 8 mo, airway eosinophil and Th2 responses to recall allergen challenge remained ～85-95% suppressed relative to saline-treated asthmatic mice. Four biweekly DC10 treatments, whether transtracheal or i.p., reduced all asthma parameters to near background by 8 wk, whereas s.c. DC10 treatments did not affect AHR but did reduce the airway Th2 responses (i.v. DC10 had no discernible effects). Repeated challenge of the DC10-treated mice with aerosolized OVA (100 μg/ml) did not reverse tolerance, but treatment with the indoleamine-2,3-dioxygenase antagonist 1-methyltryptophan or neutralizing anti-IL-10R from days 12 to 21 after DC10 therapy partially reversed tolerance (Th2 cytokine responses, but not AHR). These findings indicate that DC10-induced Th2 tolerance in asthmatic animals is long lived, but that DC10s employ distinct mechanisms to affect AHR versus Th2 immunoinflammatory parameters.     

Variation in Osmoregulation in Differentially Drought-Sensitive Wheat Genotypes Involves Calcium

Two wheat (Triticum aestivum L.) genotypes differing in their sensitivity to water deficit (stress tolerant - C306 and stress susceptible - HD2329) were subjected to osmotic stress for 7 d using polyethylene glycol (PEG-6000; osmotic potential –1.0 MPa), at initial vegetative growth. The plants were either supplemented with 1 mM CaCl₂ (Ca²⁺) alone or along with verapamil (VP; calcium channel blocker) to investigate the involvement of calcium in governing osmoregulation. Relative elongation rate (RER), dry matter (DM) production, water potential (_w), electrolyte leakage (EL), contents of proline (Pro) and glycine betaine (GB) and activities of -glutamyl kinase (GK) and proline oxidase (PO) in shoots and roots were examined during stress period. C306 showed relatively higher accumulation of Pro while HD2329 accumulated more GB under stress. RER, DM and _w were relatively higher in C306 than HD2329. Roots compared to shoots showed lower content of osmolytes but had faster rate of their accumulation. Presence of Ca²⁺ in the medium increased the activity of GK and decreased that of PO while in the presence of its inhibitor, decrease in activity of both the enzymes was observed. Ca²⁺ appeared to reduce the damaging effect of stress by elevating the content of Pro and GB, improving the water status and growth of seedlings and minimizing the injury to membranes. The protective effect of Ca²⁺ was observed to be more in HD2329 than C306.     

pH-Dependent Conformational Transitions in Conalbumin (Ovotransferrin), a Metalloproteinase from Hen Egg White

Acid unfolding pathway of conalbumin (CA), a monomeric glycoprotein from hen egg white, has been investigated using far- and near-UV CD spectroscopy, intrinsic fluorescence emission, extrinsic fluorescence probe 1-anilino-8-napthalene sulfonate (ANS) and dynamic light scattering (DLS). We observe pH-dependent changes in secondary and tertiary structure of CA. It has native-like α-helical secondary structure at pH 4.0 but loss structure at pH 3.0. The CA existed exclusively as a pre-molten globule state and molten globule state in solution at pH 4.0 and pH 3.0, respectively. The effect of pH on the conformation and thermostability of CA points toward its heat resistance at neutral pH. DLS results show that MG state existed as compact form in aqueous solutions with hydrodynamic radii of 4.7 nm. Quenching of tryptophan fluorescence by acrylamide further confirmed the accumulation of an intermediate state, partly unfolded, in-between native and unfolded states.     

Measurement of waist circumference predicts coronary atherosclerosis beyond plasma adipokines

Objective:

The association of plasma adipokines beyond waist circumference (WC) with coronary artery calcification (CAC), a measure of subclinical atherosclerosis, is unknown.

Design and Methods:

Asymptomatic Caucasian individuals from two community‐based cross‐sectional studies (n = 1,285) were examined and multivariate analysis of traditional risk factors was performed, then WC and adipokines (adiponectin and leptin) were added. Incremental value of each was tested with likelihood ratio testing.

Results:

Beyond traditional risk factors, WC (Tobit regression ratio 1.69, P < 0.001) and plasma leptin (1.57, P < 0.001) but not plasma adiponectin (P = 0.75) were independently associated with CAC. In nested models, neither adiponectin (χ² = 0.76, P = 0.38) nor leptin (χ² = 1.32, P = 0.25) added value to WC beyond traditional risk factors, whereas WC added incremental value to adiponectin (χ² = 28.02, P < 0.0001) and leptin (χ² = 13.58, P = 0.0002).

Conclusion:

In the face of important biomarkers such as plasma adiponectin and leptin, WC remained a significant predictor of CAC beyond traditional risk factors underscoring the importance of WC measurement during cardiovascular risk assessment.