Browsing by Author "Avila, Felipe"

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    3-Hydroxykynurenine bound to eye lens proteins induces oxidative modifications in crystalline proteins through a type I photosensitizing mechanism
    (2019) Avila, Felipe; Ravello, Natalia; Zanocco, Antonio L.; Gamon, Luke F.; Davies, Michael J.; Silva, Eduardo
    Photosensitized reactions mediated by endogenous chromophores have been associated with the etiology of age-related cataract disease. Endogenous chromophores such as 3-hydroxykynurenine (3OHKN) can be found in both free form, and bound to crystallin proteins. However, their efficiency in generating photo-induced oxidative modifications on eye lens proteins is not completely understood. In this work, the efficiency and photodynamic activity of 3OHKN bound to both lysine (3OHKN-Lys) and bovine lens proteins (3OHKN-BLP) was assessed and compared with the photosensitizing activity of the major chromophore arising from glucose degradation (GDC). The photosensitizing activity of 3OHKN-Lys, 3OHKN-BLP and GDC was characterized by measurement of singlet oxygen quantum yields, O-2 consumption, SDS-PAGE and amino acid analysis of the photo-oxidized proteins.
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    Photosensitized reactions mediated by the major chromophore arising from glucose decomposition, result in oxidation and cross-linking of lens proteins and activation of the proteasome
    (ELSEVIER SCIENCE BV, 2012) Avila, Felipe; Trejo, Sebastian; Baraibar, Martin A.; Friguet, Bertrand; Silva, Eduardo
    Glucose solutions incubated at low oxygen concentration gave rise to the appearance of an absorption band in the UVA-visible region after 10 days. Further characterization evidenced that this band was composed by a single chomophore with maximum absorption bands at 335 and 365 nm. HPLC/MS and UV spectroscopy assays indicated that this product is composed by five unities of furan. Importantly, the presence of a compound with identical spectral and chromatographic properties was observed in the water-soluble fraction of cataractous human eye lenses. The photo-biological effects of this glucose-derived chromophore (GDC) have been addressed using targets of biological relevance, such as water-soluble proteins from eye lens and the proteasome present in this protein mixture. Increased protein oxidation and protein crosslinking was observed when lens proteins were exposed to UVA-visible light in the presence of GDC under a 5% and 20% oxygen atmosphere. In addition, an increased proteasome peptidase activity was also observed. However, the use of D2O resulted in decreased proteasome activity, suggesting that singlet oxygen promotes the impairment of proteasome activity. Our results suggest that the species generated by Type I and Type II mechanisms have opposite effects on proteasome activity, being Type I a positive activator while Type II lead to impairment of proteasome function. (C) 2011 Elsevier B.V. All rights reserved.
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    Simultaneous chemical and photochemical protein crosslinking induced by irradiation of eye lens proteins in the presence of ascorbate: the photosensitizing role of an UVA-visible-absorbing decomposition product of vitamin C
    (ROYAL SOC CHEMISTRY, 2010) Avila, Felipe; Friguet, Bertrand; Silva, Eduardo
    Exposure to light has been implicated as a risk factor during aging of the eye lens and in cataract generation. In order to visualize the actual effect of UVA-visible light on this tissue, we incubated water-soluble eye lens proteins with ascorbate in the presence and absence of UVA-visible light for 3, 6 and 9 days at low oxygen concentration. The samples incubated in the presence of light were characterized by an initially small but continuous increase over time of the protein crosslinking. This was not the result of more extensive glycation because the decrease in amino group content of the proteins and the decomposition of ascorbate was the same in both irradiated and unirradiated samples. The augmented crosslinking capacity observed in the presence of UVA-visible light is due to the generation of a chromophore from the decomposition of ascorbate. This chromophore, obtained after 3, 6 and 9 days of incubation of solutions containing only ascorbate, induces both protein-crosslinking and oxidation after exposure to UVA-visible light in the presence of lens proteins. The extent of the crosslinking was proportional to the amount of the chomophore present in the solution. The presence of this chromophore was also determined when ascorbate was incubated with four-fold higher concentrations of N-alpha-acetyl lysine and N-alpha-acetyl arginine. When these samples were used as photosensitizers, the crosslinking degree was conditioned by the presence of this chromophore; nonetheless, the ascorbate-mediated advanced glycation end product (AGE) generation also made a contribution. The results of this work indicate that ascorbate oxidation, which generates the AGEs responsible for the chemical crosslinking of the lens proteins, also simultaneously produces a chromophore that can act as a photosensitizer, further increasing the protein crosslinking.
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    Thermal treatment under oxidative conditions increases the antioxidant and antiglycation activity of Chilean Tortola beans ( Phaseolus vulgaris)
    (2025) Cruz, Nadia; Basoalto-Cubillos, Aracely; Marquez, Katherine; Nina, Nelida; Vallejos-Almirall, Alejandro; Armijo, Francisco; Schmeda-Hirschmann, Guillermo; Avila, Felipe
    The influence of oxygen on the thermal treatment (TT) of secondary metabolite-enriched extracts (SMEEs) from T & oacute;rtola beans and procyanidin C1 (PC1) on the inhibition of advanced glycation end products (AGEs) generation in proteins was investigated. SMEE was incubated at 4 degrees C (control) or thermally treated at 60 degrees C for 2 h, at either 0 % O-2 (I) or 20 % O-2 (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 % O-2 generated procyanidin dimers and tetramers. PC1 TT at 20 % O-2 exhibited higher oxidation potentials and lower IC50 values of fluorescent AGEs than those of controls or TT at 0 % O-2. These findings indicate that SMEE from T & oacute;rtola beans after treatment II changes the degree of polymerization and oxidation procyanidins, thereby increasing their antiglycation activity.