N-Terminal 2,3-diaminopropionic acid (Dap) peptides as efficient methylglyoxal scavengers to inhibit advanced glycation endproduct (AGE) formation

A novel multi-target strategy to attenuate the progression of Parkinson's disease by diamine hybrid AGE/ALE inhibitor

Instead of a conventional 'one-drug-one-target approach', this article presents a novel multi-target approach with a concept of trapping simultaneously as many detrimental factors as possible involved in the progression of Parkinson's disease. These factors include reactive carbonyl species, reactive oxygen species, Fe^3+/Cu²⁺ and ortho-quinones (o-quinone), in particular. Different from the known multi-target strategies for Parkinson's disease, it is a sort of 'vacuum cleaning' strategy. The new agent consists of reactive carbonyl species scavenging moiety and reactive oxygen species scavenging and metal chelating moiety linked by a spacer. Provided that the capacity of scavenging o-quinones is demonstrated, this type of agent can further broaden its potential therapeutic profile. In order to support this new hypothetical approach, a number of simple in vitro experiments are proposed.

Multifunctional diamine AGE/ALE inhibitors with potential therapeutical properties against Alzheimer's disease

An important part of pathogenesis of Alzheimer's disease (AD) is attributed to the contribution of AGE (Advanced Glycation Endproducts) and ALE (Advanced Lipid peroxidation Endproducts). In order to attenuate the progression of AD, we designed a new type of molecules that consist of two trapping parts for reactive carbonyl species (RCS) and reactive oxygen species (ROS), precursors of AGE and ALE, respectively. These molecules also chelate transition metals, the promoters of ROS formation. In this paper, synthesis of the new AGE/ALE inhibitors and evaluation of their physicochemical and biological properties (carbonyl trapping capacity, antioxidant activity, Cu(2+)-chelating capacity, cytotoxicity and protective effect against in vitro MGO-induced apoptosis in the model AD cell-line PC12) are described. It is found that compounds 40b and 51e possess promising therapeutic potentials for treating AD.

Targeting Reactive Carbonyl Species with Natural Sequestering Agents

Reactive carbonyl species generated by the oxidation of polyunsaturated fatty acids and sugars are highly reactive due to their electrophilic nature, and are able to easily react with the nucleophilic sites of proteins as well as DNA causing cellular dysfunction. Levels of reactive carbonyl species and their reaction products have been reported to be elevated in various chronic diseases, including metabolic disorders and neurodegenerative diseases. In an effort to identify sequestering agents for reactive carbonyl species, various analytical techniques such as spectrophotometry, high performance liquid chromatography, western blot, and mass spectrometry have been utilized. In particular, recent advances using a novel high resolution mass spectrometry approach allows screening of complex mixtures such as natural products for their sequestering ability of reactive carbonyl species. To overcome the limited bioavailability and bioefficacy of natural products, new techniques using nanoparticles and nanocarriers may offer a new attractive strategy for increased in vivo utilization and targeted delivery of bioactives.

Compounds blocking methylglyoxal-induced protein modification and brain endothelial injury

BACKGROUND AND AIMS

Elevated levels of reactive carbonyl species such as methylglyoxal triggers carbonyl stress and activates a series of inflammatory responses leading to accelerated vascular damage. Carbonyl stress is implicated in conditions and diseases like aging, diabetes mellitus, Alzheimer's disease and cardiovascular diseases. Our aim was to examine the effects of methylglyoxal on human hCMEC/D3 brain endothelial cells and search for protective molecules to prevent endothelial damage.

METHODS

Methylglyoxal-induced modification of albumin was tested in a cell-free assay. Endothelial cell viability was monitored by impedance measurement in real-time. The following compounds were tested in cell-free and viability assays: β-alanine, all-trans-retinoic acid, aminoguanidine, ascorbic acid, L-carnosine, GW-3333, indapamide, piracetam, γ-tocopherol, U0126, verapamil. Barrier function of brain endothelial monolayers was characterized by permeability measurements and visualized by immunohistochemistry for β-catenin. mRNA expression level of 60 selected blood-brain barrier-related genes in hCMEC/D3 cells was investigated by a custom Taqman gene array.

RESULTS

Methylglyoxal treatment significantly elevated protein modification, exerted toxicity, reduced barrier integrity, increased permeability for markers FITC-dextran and albumin and caused higher production of reactive oxygen species in hCMEC/D3 endothelial cells. Changes in the mRNA expression of 30 genes coding tight junction proteins, transporters and enzymes were observed in methylglyoxal-treated hCMEC/D3 cells. From the tested 11 compounds only all-trans-retinoic acid, an antioxidant and antiglycation agent, U0126, a MAP/ERK kinase inhibitor and aminoguanidine attenuated methylglyoxal-induced damage in hCMEC/D3 cells.

CONCLUSIONS

All-trans-retinoic acid and inhibition of the MAP/ERK signaling pathway may be protective in carbonyl stress induced brain endothelial damage.

A novel high resolution MS approach for the screening of 4-hydroxy-trans-2-nonenal sequestering agents

An in vitro high resolution mass spectrometry (MS) method was set-up to test the ability of compounds, mixtures and extracts to inhibit protein carbonylation induced by reactive carbonyl species (RCS). The method consists of incubating the protein target (ubiquitin) with 4-hydroxy-trans-2-nonenal (HNE) in the presence and absence of the tested compound. After 24h of incubation, the reaction is stopped and the protein is analyzed by high-resolution MS. The extent of protein carbonylation is determined by measuring the area of the +11 multicharged peak of the HNE adduct in respect to the native form. The method was validated by measuring the effect of well-known RCS sequestering agents, namely aminoguanidine, pyridoxamine, hydralazine and carnosine, yielding a good reproducibility and the possibility to be automatable. All the compounds were found to dose-dependently inhibit the protein carbonylation with the following order of potency carnosine≈hydralazine≫aminoguanidine>pyridoxamine, as determined by calculating the UC50 values, that is the concentration required to inhibit ubiquitin carbonylation by 50%. A good correlation was found with the results obtained by measuring HNE consumption using an HPLC method optimized by a mobile phase set at pH 7.4, in order to stabilize the eluted adducts. The MS approach was then applied to test the effect of two selected natural extracts on protein carbonylation, i.e. green coffee bean extract and procyanidins from Vitis vinifera. In summary, this paper reports a validated and highly reproducible MS method to test the ability of pure compounds as well as natural extracts to act as protein carbonylation inhibitors.

Molecular strategies to prevent, inhibit, and degrade advanced glycoxidation and advanced lipoxidation end products

The advanced glycoxidation end products (AGEs) and lipoxidation end products (ALEs) contribute to the development of diabetic complications and of other pathologies. The review discusses the possibilities of counteracting the formation and stimulating the degradation of these species by pharmaceuticals and natural compounds. The review discusses inhibitors of ALE and AGE formation, cross-link breakers, ALE/AGE elimination by enzymes and proteolytic systems, receptors for advanced glycation end products (RAGEs) and blockade of the ligand-RAGE axis.

Protective effects of hesperidin derivatives and their stereoisomers against advanced glycation end-products formation

CONTEXT

Maillard reaction is implicated in the development of pathophysiology in age-related diseases. The search for newer Maillard reaction inhibitors is a priority among strategies to combat diabetes complications.

OBJECTIVE

To evaluate the inhibitory potential of hesperidin, its derivatives and their stereoisomers against advanced glycation end-products (AGEs) formation.

MATERIALS AND METHODS

Hesperidin and hesperetin were chirally separated and the inhibitory effects of 1:1 mixture of (2S)- and (2R)-hesperidin (1), (2S)-hesperidin (2), (2R)-hesperidin (3), 1:1 mixture of (S)- and (R)-hesperetin (4), (S)-hesperetin (5), (R)-hesperetin (6), and monoglucosyl hesperidin (7) [1:1 mixture of (2S)-glucosyl hesperidin (8) and (2R)-glucosyl hesperidin (9)] at a concentration of 1 mM on protein glycation reaction have been revealed using the newly constructed RNase A-methylglyoxal (MGO) assay for the early stage and the bovine serum albumin (BSA)-glucose assay for the late stage of Maillard reaction.

RESULTS

This study has demonstrated that hesperidin and its derivatives possessed relatively strong activity against the formation of AGEs. (S)-Hesperetin (5) possessed the highest inhibitory rate up to 57.4% in BSA-glucose assay, 38.2% in RNase A-MGO assay.

DISCUSSION AND CONCLUSION

The new RNase A-MGO assay system could be used for the screening of AGEs inhibitors and hesperidin, and its derivatives could be promising candidate adjuvants for the treatment of diabetes complication, and age-related chronic diseases.

Methylglyoxal has deleterious effects on thioredoxin in human aortic endothelial cells

Methylglyoxal (MG), a precursor of advanced glycation end products (AGEs), is elevated in diabetic patient's plasma. Some studies have demonstrated that MG induces oxidative stress and apoptosis. Thioredoxin (Trx) is a cytoprotective protein with anti-oxidative and anti-apoptosis functions. In this study, we examined the effects of MG on Trx in human aortic endothelial cells (HAECs). MG increased oxidized-hydroethidine fluorescence intensity, suggesting intracellular accumulation of reactive oxygen species. Flow cytometric analyses with annexin-V/propidium iodide double staining revealed that cells incubated with MG displayed features characteristic of apoptosis. The condensation of chromatin, the release of cytochrome c into cytosol, and the collapse of mitochondrial membrane potential by MG were observed. The exposure to MG decreased Trx protein levels through transcription regulation. MG induced the oxidative damage of peroxiredoxin, a Trx-dependent peroxidase. These results suggest that MG has deleterious effects on Trx in HAECs, which may be contribute to oxidative stress and apoptosis.

Transforming dietary peptides in promising lead compounds: the case of bioavailable carnosine analogs

The ability of carnosine to prevent advanced glycoxidation end products (AGEs) and advanced lipoxidation end products (ALEs) formation, on the one hand, and the convincing evidence that these compounds act as pathogenetic factors, on the other hand, strongly support carnosine as a promising therapeutic agent for oxidative-based diseases. The mechanism/s by which carnosine inhibits AGEs and ALEs is still under investigation but an emerging hypothesis is that carnosine acts by deactivating the AGEs and ALEs precursors and in particular the reactive carbonyl species (RCS) generated by both lipid and sugar oxidation. The ability of carnosine to inhibit AGEs and ALEs formation and the corresponding biological effects has been demonstrated in several in vitro studies and in some animal models. However, such effects are in line of principle, limited in humans, due to the effect of serum carnosinase (absent in rodents), which catalyzes the carnosine hydrolysis to its constitutive amino acids. Such a limitation has prompted a great interest in the design of carnosine derivatives, which maintaining (or improving) the reactivity with RCS, are more resistant to carnosinase. The present paper intends to critically review the most recent studies oriented to obtaining carnosine derivatives, optimized in terms of reactivity with RCS, selectivity (no reaction with physiological aldehydes) and the pharmacokinetic profile (mainly through an enhanced resistance to carnosinase hydrolysis). The review also includes a brief description of AGEs and ALEs as drug targets and the evidence so far reported regarding the ability of carnosine as inhibitor of AGEs and ALEs formation and the proposed reaction mechanisms.