DSC characterization of rabbit corneas treated with Stryphnodendron adstringens (Mart.) Coville extracts

Abstract

Keratoconus is an eye ectasia that affects the cornea causing distortion of vision. Corneal crosslinking promoted by riboflavin photo-stimulated at 365 nm is a treatment used successfully to block the keratoconus progression. In this study, we characterize rabbit corneas subjected to enhanced crosslinking using different vegetable extracts prepared from Stryphnodendron adstringens (Mart.) Coville bark by differential scanning calorimetry. The extracts tested in this study were: aqueous, ketonic, ethanolic, ethyl acetate and hydroalcoholic, which revealed high levels of polyphenols, such as proanthocyanidins. The corneas, obtained from the slaughter rabbits, were divided into groups: control (consisting of untreated corneal samples) and S. adstringens, where the samples were subjected to 4% vegetable extracts for 2 h. The DSC profiles of the corneas were obtained in nitrogen atmosphere. The results showed that temperature and enthalpy of denaturation of the corneal samples treated with S. adstringens were higher than the control group. The control group presents temperature and enthalpy values of 59.8 ± 1.1 °C and 24.6 ± 2.7 J g -1 , respectively. After crosslinking with ketone extract, the values were 90.1 ± 1.1 °C and 39.9 ± 2.7 J g -1 . These results show that S. adstringens is efficient to increment the crosslinking level of the corneas.

Thermal stability of collagen in naturally ageing and in vitro glycated rabbit tissues

“…In other studies, no immunoreactivity to different types of AGEs was detected in normal human corneas in adults of different age [40] and in healthy corneas in monkeys [41]. As concerns thermal denaturation of cornea, very little literature exists [27,39] and the only one reporting age-related changes [39] shows rather a slight decrease in denaturation temperature without any signs of age-related corneal crosslinking. The lack of glycation evidence in naturally ageing corneal samples can result from a relatively short half-life of type I collagen in cornea [37] or could be a sign of low susceptibility to AGEs formation under normal conditions.…”

“…The main macromolecule of extracellular matrix in these tissues is type I collagen, even though the other components and the structure of the matrix are different [35][36][37]. Collagen in tissues was frequently characterized in the terms of thermal denaturation parameters [24][25][26][27][28][29][30][31][32], and in particular, differences in temperature of denaturation were used as an Table 2 Parameters of thermal denaturation of cornea from young adult (Y-) and ageing (A-) rabbits incubated in ribose solution (-R) and in buffer (-B) Mean values (standard deviation) are listed; n = 6 in each group p values for significance of differences between -B and -R samples calculated from paired t test Thermal stability of collagen in naturally ageing and in vitro glycated rabbit tissues 1907 indicator of differences in collagen crosslinking on the basis of numerous reports from previous experiments [17,18,20,21,25,27,38]. The temperature of denaturation in corneal samples was not different between young mature (Y-C) and ageing (A-C) groups (Table 1).…”

“…Parameters of thermal denaturation are also very sensitive to hydration of collagen fibres [22][23][24]. The thermal studies of collagens were conducted using model collagen-like peptides [14], collagens extracted from tissues [17,18,22,23,25] and on tissue collagens in situ [24][25][26][27][28][29][30][31][32]. Tissues from musculoskeletal system were the most frequently examined [24-26, 28, 29, 32], and thermal parameters of collagen denaturation were shown to be related to different types of the tissues disorders.…”

Second Harmonic Generation Signals in Rabbit Sclera As a Tool for Evaluation of Therapeutic Tissue Cross-linking (TXL) for Myopia

“…Cut the remaining 3 sectors from both lateral sides (i.e., nasal and temporal), and the bottom. NOTE: the numbering of the sectors (1-4) which are further divided into squares (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16) is demonstrated in Figure 1A Figure 1A, in order to localize the distance of the analyzed tissue from the location of the injected area. 4.…”

“…During heating in the DSC, a critical transition temperature is achieved that results in denaturation of the collagen molecule, resulting in uncoiling of the triple helix, a process that forms what is commonly known as gelatin. This thermal denaturation disrupts hydrogen bonds along the collagen molecule and can be shifted to higher temperatures through induced cross-linking methods 12,13 . This method has been used for many decades, particularly in the biomaterials industry and for processes that include leather-making.…”