Effect of spermine-derived AGEs on oxidative stress and polyamine metabolism.

Non-enzymatic glycation between proteins and carbohydrates, such as advanced glycation end products (AGEs), are naturally occurring compounds implicated in aging and numerous degenerative diseases. Methyl glyoxal (MG), which is an intermediate of the AGE biosynthetic pathway, is known to react with primary amines of proteins to create a wide range of AGE modifications, such as carboxyethyl lysine (CEL) and methylglyoxal-derived lysine dimer (MOLD). As a means to investigate and probe the ROS production pathways of AGEs, low molecular weight compounds carboxyethyl spermine (CES) and methylglyoxal-derived spermine dimer (MOSD) were synthesized, which replace lysine with another highly nucleophilic biological amine, spermine (SPM). Contrary to expectations, results show CES- and MOSD-induced oxidative stress proceeds through different pathways. As such, we have developed useful probes that can be used to better understand and investigate pathways related to acrolein-based oxidative stress and/or polyamine metabolic pathways.

In vivo imaging of advanced glycation end products (AGEs) of albumin: first observations of significantly reduced clearance and liver deposition properties in mice.

Advanced glycation end products (AGEs) are associated with various diseases, especially during aging and the development of diabetes and uremia. To better understand these biological processes, investigation of the in vivo kinetics of AGEs, i.e., analysis of trafficking and clearance properties, was carried out by molecular imaging. Following the preparation of Cy7.5-labeled AGE-albumin and intravenous injection in BALB/cA-nu/nu mice, noninvasive fluorescence kinetics analysis was performed. In vivo imaging and fluorescence microscopy analysis revealed that non-enzymatic AGEs were smoothly captured by scavenger cells in the liver, i.e., Kupffer and other sinusoidal cells, but were unable to be properly cleared from the body. Overall, these results highlight an important link between AGEs and various disorders associated with them, which may serve as a platform for future research to better understand the processes and mechanisms of these disorders.

A cascading reaction sequence involving ligand-directed azaelectrocyclization and autooxidation-induced fluorescence recovery enables visualization of target proteins on the surfaces of live cells.

A general probe designed to induce a cascading sequence of reactions on a target protein was efficiently synthesized. The cascading reaction sequence involved (i) ligand-directed azaelectrocyclization with lysine and (ii) the autooxidation-induced release of a fluorescence quencher from the labeled protein. The probe was linked to a cyclic RGDyK peptide to enable the selective visualization of integrin αVß3 on the surfaces of live cells.

Polyamine modification by acrolein exclusively produces 1,5-diazacyclooctanes: a previously unrecognized mechanism for acrolein-mediated oxidative stress.

Acrolein, a toxic unsaturated aldehyde generated as a result of oxidative stress, readily reacts with a variety of nucleophilic biomolecules. Polyamines, which produced acrolein in the presence of amine oxidase, were then found to react with acrolein to produce 1,5-diazacyclooctane, a previously unrecognized but significant downstream product of oxidative stress. Although diazacyclooctane formation effectively neutralized acrolein toxicity, the diazacyclooctane hydrogel produced through a sequential diazacyclooctane polymerization reaction was highly cytotoxic. This study suggests that diazacyclooctane formation is involved in the mechanism underlying acrolein-mediated oxidative stress.

2,6,9-Triazabicyclo[3.3.1]nonanes as overlooked amino-modification products by acrolein.

The reaction of several primary amines with acrolein smoothly provided the corresponding 2,6,9-triazabicyclo[3.3.1]nonanes through a formal [4 + 4] reaction of the intermediary unsaturated imines. The reactivity profiles in aqueous media and the results from cytotoxic activity assays suggested that the caged products may be relevant in biological systems and may contribute to the mechanisms underlying the oxidative stress response to acrolein.

5-O-Mycaminosyltylonolide antibacterial derivatives: design, synthesis and bioactivity.

Tylosin is a 16-membered macrolide broad-spectrum antibiotic that has an important role in veterinary medicine, active against Gram-positive and a restricted range of Gram-negative bacteria. We synthesized 15 types of tylosin-related derivatives by chemical modification and evaluated them against mastitis pathogens. Among them, 20-deoxy-20-{N-methyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2f and 20-deoxy-20-{N-benzyl-N-[1-(3-quinolyl)-1H-1,2,3-triazol-4-yl]methylamino}-5-O-mycaminosyltylonolide 2k were found to not only expand their antibacterial impact to include Gram-negative bacteria, such as Escherichia coli and Klebsiella pneumoniae, but also to retain or increase antibacterial activity against Gram-positive bacteria, such as Staphylococcus aureus and Streptococcus uberis in comparison with the parent tylosin.

1,5-Diazacyclooctanes, as Exclusive Oxidative Polyamine Metabolites, Inhibit Amyloid-ß(1-40) Fibrillization.

Biologically relevant 1,5-diazacyclooctanes derived from polyamines and acrolein, inhibit Aß40 peptide fibrillization and significantly suppress cell cytotoxicity. Formal [4+4] cycloaddition reaction of imines is thus involved in modulating oxidative stress processes associated with neural diseases.

Identification of bound water molecules in the cyclic tetrasaccharide, cyclo-{-->6}-alpha-d-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->).

A structural characterization of bound water molecules in the cyclic tetrasaccharide, cyclo-{-->6}-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->), was carried out by NMR spectroscopy. H-1', 2'-OH, H-3', and 4'-OH of the 3-O-glycosylated residue and H-1 of the 6-O-glycosylated residue were found to cross-relax with protons of bound waters using the double-pulsed field-gradient spin-echo ROESY experiment. In the crystal structure, one water molecule is located in the center of the plate, and its temperature factor is very low, indicating that this water molecule is an intrinsic component.

Observation of 1,6-anhydro-beta-maltose and 1,6-anhydro-beta-D-glucopyranose complexed with rubidium by NMR spectroscopy and electrospray ionization mass spectrometry.

A complex of 1,6-anhydro-beta-maltose with rubidium and that of 1,6-anhydro-beta-D-glucopyranose with rubidium were characterized using 87Rb NMR spectroscopy, diffusion-ordered NMR spectroscopy (DOSY) and electrospray ionization mass spectrometry (ESI-MS). Although subtle differences were observed in the 1H chemical shifts of 1,6-anhydro-beta-maltose in between the presence and absence of rubidium in deuterium oxide, measurements of the spin-lattice relaxation time (T1) of the 87Rb nucleus, the diffusion coefficients of 1,6-anhydro-beta-maltose using 1H DOSY and ESI-MS indicated the complex formation of 1,6-anhydro-beta-maltose with rubidium. The complex formation with rubidium was also identified for 1,6-anhydro-beta-D-glucopyranose using NMR and ESI-MS techniques.

Practical aspects of ROESY experiments for identification of bound waters in the cyclic tetrasaccharide.

ROESY pulse sequences are presented and evaluated to identify bound waters in the cyclic tetrasaccharide. The first experiment incorporated the double-pulsed field gradient spin-echo (DPFGSE) for selective water excitation at the initial portion of the pulse sequence. Although long, shaped pulses were used in DPFGSE to achieve the highly selective excitation of water resonance that is very close to resonances of the cyclic tetrasaccharide, the approach was not effective because of the loss of sensitivity. Concomitant use of long delays and moderate length of shaped pulses in the portion of DPFGSE gained more sensitivity. A simple approach incorporating spin-echo with long delays instead of DPFGSE also afforded a sensitive spectrum. Practical aspects of these ROESY experiments are illustrated using the cyclic tetrasaccharide cyclo-{-->6}-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->6)-alpha-D-Glcp-(1-->3)-alpha-D-Glcp-(1-->).