3-Hydroxykynurenine bound to eye lens proteins induces oxidative modifications in crystalline proteins through a type I photosensitizing mechanism

Thermal treatment under oxidative conditions increases the antioxidant and antiglycation activity of Chilean Tórtola beans (Phaseolus vulgaris)

The influence of oxygen on the thermal treatment (TT) of secondary metabolite-enriched extracts (SMEEs) from Tórtola beans and procyanidin C1 (PC1) on the inhibition of advanced glycation end products (AGEs) generation in proteins was investigated. SMEE was incubated at 4 °C (control) or thermally treated at 60 °C for 2 h, at either 0 % O2 (I) or 20 % O2 (II). Treatments I and II increased the content of procyanidin dimers B2. Treatment II was more effective than the control or treatment I in preventing homocysteine oxidation and AGEs generation. TT of PC1 at 0 % or 20 % O2 generated procyanidin dimers and tetramers. PC1 TT at 20 % O2 exhibited higher oxidation potentials and lower IC50 values of fluorescent AGEs than those of controls or TT at 0 % O2. These findings indicate that SMEE from Tórtola beans after treatment II changes the degree of polymerization and oxidation procyanidins, thereby increasing their antiglycation activity.

Use of photosensitive molecules in the crosslinking of biopolymers: applications and considerations in biomaterials development

The development of diverse types of biomaterials has significantly contributed to bringing new biomedical strategies to treat clinical conditions. Applications of these biomaterials can range from mechanical support and protection of injured tissues to joint replacement, tissue implants, and drug delivery systems. Among the strategies commonly used to prepare biomaterials, the use of electromagnetic radiation to initiate crosslinking stands out. The predominance of photo-induced polymerization methods relies on a fast, efficient, and straightforward process that can be easily adjusted to clinical needs. This strategy consists of irradiating the components that form the material with photons in the near ultraviolet-visible wavelength range (i.e., ∼310 to 750 nm) in the presence of a photoactive molecule. Upon photon absorption, photosensitive molecules can generate excited species that initiate photopolymerization through different reaction mechanisms. However, this process could promote undesired side reactions depending on the target zone or treatment type (e.g., oxidative stress and modification of biomolecules such as proteins and lipids). This review explores the basic concepts behind the photopolymerization process of ex situ and in situ biomaterials. Particular emphasis was put on the photosensitization initiated by the most employed photosensitizers and the photoreactions that they mediate in aqueous media. Finally, the undesired oxidation reactions at the bio-interface and potential solutions are presented.

Significance of Singlet Oxygen Molecule in Pathologies

Reactive oxygen species, including singlet oxygen, play an important role in the onset and progression of disease, as well as in aging. Singlet oxygen can be formed non-enzymatically by chemical, photochemical, and electron transfer reactions, or as a byproduct of endogenous enzymatic reactions in phagocytosis during inflammation. The imbalance of antioxidant enzymes and antioxidant networks with the generation of singlet oxygen increases oxidative stress, resulting in the undesirable oxidation and modification of biomolecules, such as proteins, DNA, and lipids. This review describes the molecular mechanisms of singlet oxygen production in vivo and methods for the evaluation of damage induced by singlet oxygen. The involvement of singlet oxygen in the pathogenesis of skin and eye diseases is also discussed from the biomolecular perspective. We also present our findings on lipid oxidation products derived from singlet oxygen-mediated oxidation in glaucoma, early diabetes patients, and a mouse model of bronchial asthma. Even in these diseases, oxidation products due to singlet oxygen have not been measured clinically. This review discusses their potential as biomarkers for diagnosis. Recent developments in singlet oxygen scavengers such as carotenoids, which can be utilized to prevent the onset and progression of disease, are also described.

Photosensitization Reactions of Biomolecules: Definition, Targets and Mechanisms

Photosensitization reactions have been demonstrated to be largely responsible for the deleterious biological effects of UV and visible radiation, as well as for the curative actions of photomedicine. A large number of endogenous and exogenous photosensitizers, biological targets and mechanisms have been reported in the past few decades. Evolving from the original definitions of the type I and type II photosensitized oxidations, we now provide physicochemical frameworks, classifications and key examples of these mechanisms in order to organize, interpret and understand the vast information available in the literature and the new reports, which are in vigorous growth. This review surveys in an extended manner all identified photosensitization mechanisms of the major biomolecule groups such as nucleic acids, proteins, lipids bridging the gap with the subsequent biological processes. Also described are the effects of photosensitization in cells in which UVA and UVB irradiation triggers enzyme activation with the subsequent delayed generation of superoxide anion radical and nitric oxide. Definitions of photosensitized reactions are identified in biomolecules with key insights into cells and tissues.

Antiglycating Effect of Phenolics from the Chilean Currant Ribes cucullatum under Thermal Treatment

Numerous dietary polyphenols possess antiglicating activity, but the effects of thermal treatment on this activity are mostly unknown. The effect of thermal treatment in the antiglycating activity of polyphenolic enriched extracts (PEEs) from Ribes cucullatum towards glyoxal-induced glycation of sarcoplasmic proteins was assessed. Sarcoplasmic proteins from chicken, beef, salmon, and turkey, were incubated 2 h at 60 °C with and without glyoxal and different concentrations of PEEs (0.25, 0.5, 1, and 5 mg/mL). The antiglycating activity was evaluated by: (1) Lys and Arg consumption, (2) Carboxymethyl lysine (CML) generation, and (3) lipid-derived electrophiles inhibition in a gastric digestion model. Protective effects were observed against CML generation in proteins and a decrease of electrophiles in the gastric digestion model. A dose-dependent consumption of Lys and Arg in proteins/PEEs samples, indicated the possible occurrence of quinoproteins generation from the phenolics. Protein/PEEs incubations were assessed by: (1) High pressure liquid chromatography analysis, (2) Gel electrophoresis (SDS-PAGE), and (3) Redox cycling staining of quinoproteins. Protein/PEEs incubations produced: (1) Decrease in phenolics, (2) increase of protein crosslinking, and (3) dose-dependent generation of quinoproteins. We demonstrate that phenolic compounds from R. cucullatum under thermal treatment act as antiglycating agents, but oxidative reactions occurs at high concentrations, generating protein crosslinking and quinoproteins.

Pharmaceutical Excipients Enhance Iron-Dependent Photo-Degradation in Pharmaceutical Buffers by near UV and Visible Light: Tyrosine Modification by Reactions of the Antioxidant Methionine in Citrate Buffer

PURPOSE

To evaluate the effect of excipients, including sugars and amino acids, on photo-degradation reactions in pharmaceutical buffers induced by near UV and visible light.

METHODS

Solutions of citrate or acetate buffers, containing 1 or 50 μM Fe³⁺, the model peptides methionine enkephalin (MEn), leucine enkephalin (LEn) or proctolin peptide (ProP), in the presence of commonly used amino acids or sugars, were photo-irradiated with near UV or visible light. The oxidation products were analyzed by reverse-phase HPLC and HPLC-MS/MS.

RESULTS

The sugars mannitol, sucrose and trehalose, and the amino acids Arg, Lys, and His significantly promote the oxidation of peptide Met to peptide Met sulfoxide. These excipients do not increase the yields of hydrogen peroxide, suggesting that other oxidants such as peroxyl radicals are responsible for the oxidation of peptide Met. The addition of free Met reduces the oxidation of peptide Met, but, in citrate buffer, causes the addition of Met oxidation products to Tyr residues of the target peptides.

CONCLUSIONS

Commonly used excipients enhance the light-induced oxidation of amino acids in model peptides.

Near UV and Visible Light Induce Iron-Dependent Photodegradation Reactions in Pharmaceutical Buffers: Mechanistic and Product Studies

Near UV (λ = 320-400 nm) and visible light (λ = 400-800 nm) can lead to the oxidation of pharmaceutical proteins, which can affect efficiency and promote immunogenicity. However, no concise mechanism has been established for the photo-oxidation of pharmaceutical proteins under near UV and visible light. Here, we show that carboxylic acid buffer-Fe³⁺ complexes can function as photosensitizers, causing peptide degradation via the formation of various radicals and oxidants. Three pharmaceutical relevant carboxylic acid buffers (citrate, acetate, and succinate) were tested under near UV and visible light. Oxidation reactions were monitored for model peptides containing readily oxidizable amino acids, such as methionine- or leucine-enkephalin and proctolin peptide. Oxidation products were evaluated by RP-HPLC coupled to UV or fluorescent detection and RP-HPLC-MS/MS. Specifically for citrate buffer, the light-induced formation of H₂O₂, ^•OH, ^•CO₂^-, and formaldehyde was demonstrated. The peptides displayed oxidation of Met, hydroxylation of Tyr and Phe, as well as the formation of novel products from Tyr. Experiments with ¹⁸O₂ resulted in the incorporation of ¹⁸O into various reaction products, consistent with a metal-catalyzed activation of O₂ into reactive oxygen species. The addition of EDTA and DTPA did not prevent the oxidation of the peptides and, in some cases, enhanced the oxidation. Our results demonstrate that pharmaceutical buffer-Fe³⁺ complexes, exposed to UV and visible light, can promote various pathways of oxidation reactions in pharmaceutical formulations.

Effect of advanced glycation end products on platelet activation and aggregation: a comparative study of the role of glyoxal and methylglyoxal

Advanced glycation end products (AGEs) arising from dietary intake have been associated with numerous chronic diseases including cardiovascular diseases. The interaction between platelets and AGEs has been proposed to play a role in the etiology of cardiovascular diseases. However, the effects of the interaction between platelets and Maillard reaction products generated from glyoxal (Gly) or methylglyoxal (MG) are poorly understood. In this work, the effects of AGEs generated by the reaction between Gly or MG with Lys or bovine serum albumin (BSA) on platelet activation and aggregation were assessed. AGEs were generated incubating Gly or MG with Lys or BSA during 5 hours or 14 days, respectively. AGEs generation were characterized by kinetic studies and by amino acid analysis. Human platelet-rich plasma (PRP) was incubated with different concentrations of AGEs from Lys-MG or Lys-Gly and BSA-MG or BSA-Gly. Platelet activation was determined quantifying the expression of CD62 (P-selectin) in PRP exposed to different AGEs concentrations. It was found that Lys-MG and Lys-Gly induced an increase in P-selectin expression (p < .05), being 33.9% higher for Lys-MG when compared to Lys-Gly. Platelets incubated in the presence of BSA-MG and BSA-Gly did not show an increase in the P-selectin expression. Platelet aggregation was significantly higher for the mixture Lys-MG (in all the range of concentrations evaluated), whereas for Lys-Gly it was only significant the highest concentration (Lys 168 µM/Gly 168 µM). It was observed a significant increase in platelet aggregation induced by ADP for samples BSA-Gly. AGEs formed with MG-Lys induce a higher activation and aggregation of platelets when compared to those formed from Gly-Lys.

Photo-oxidation of lysozyme triggered by riboflavin is O2-dependent, occurs via mixed type 1 and type 2 pathways, and results in inactivation, site-specific damage and intra- and inter-molecular crosslinks

Photosensitized protein oxidation is a promising tool for medical procedures such as photochemical tissue bonding (PTB). We have recently reported that the binding of rose Bengal, a sensitizer employed in PTB, to lysozyme modulates the photooxidation and crosslinking of this protein. In this work we examined the photooxidation and crosslinking of lysozyme mediated by riboflavin (RF) an endogenous sensitizer also employed in PTB. We hypothesized that since RF does not bind strongly to proteins, the mechanism(s) and extent of enzymatic inactivation, amino acid modification and protein crosslinking would be dependent on the presence of O₂, and differ to that induced by rose Bengal. This hypothesis was tested using UV-visible spectrophotometry, isothermal titration calorimetry (ITC), SDS-PAGE gels, quantification of amino acid consumption, and LC-MS analysis of sites of modification and crosslinks. Under N₂, limited damage was detected arising from type 1 (radical) chemistry with formation of specific intra- (Tyr20-Tyr23) and inter- (Tyr23-Trp108) molecular crosslinks. In contrast, the presence of O₂ triggered extensive protein damage through mixed type 1 and type 2 (¹O₂) mechanisms leading to Trp, Met, Tyr and His oxidation, loss of enzymatic activity and protein dimerization. LC-MS analysis provided evidence for crosslinking via radical-radical recombination reactions (Trp28-Tyr53), and secondary reactions involving nucleophilic attack of the side-chain amine of Lys116 on carbonyl groups. Overall, this behavior is in marked contrast to that detected with rose Bengal indicating that the mechanisms and sites of photo-oxidative damage, and consequences for protein function, can be modulated by the choice of sensitizing dye.

Photo-induced protein oxidation: mechanisms, consequences and medical applications

Irradiation from the sun has played a crucial role in the origin and evolution of life on the earth. Due to the presence of ozone in the stratosphere most of the hazardous irradiation is absorbed, nonetheless UVB, UVA, and visible light reach the earth’s surface. The high abundance of proteins in most living organisms, and the presence of chromophores in the side chains of certain amino acids, explain why these macromolecules are principal targets when biological systems are illuminated. Light absorption triggers the formation of excited species that can initiate photo-modification of proteins. The major pathways involve modifications derived from direct irradiation and photo-sensitized reactions. In this review we explored the basic concepts behind these photochemical pathways, with special emphasis on the photosensitized mechanisms (type 1 and type 2) leading to protein oxidation, and how this affects protein structure and functions. Finally, a description of the photochemical reactions involved in some human diseases, and medical applications of protein oxidation are presented.