In vitro human serum albumin glycation monitored by Terahertz spectroscopy

Abstract

The nonenzymatic attachment of sugars to proteins, namely glycation, is accelerated under diabetic conditions. Monitoring the glycated human serum albumin (HSA) levels gives the short term variation of glucose concentration in diabetic patients blood. Therefore, a significant effort was made to measure glycated HSA, including by spectroscopic methods such as Raman. Here we used THz spectroscopy to monitor HSA glycation in time (over 5, 7 and 11 weeks). Different sugar types have different reactivity; therefore we also addressed the reducing sugar influence on glycation by performing in vitro HSA glycation by both glucose and fructose. Since residues protonation state influences their susceptibility for glycation, we incubated HSA with sugars at two pH values: 7 and 8. Our results show that THz absorption decreases with the incubation time of HSA with sugars. At the incubation times we considered, the most significant differences were obtained on HSA samples glycated using glucose. Differences between samples glycated by glucose and by fructose show that glycation by glucose is a slower process. At pH 7, glycation by glucose is slower than at pH 8, while glycation by fructose is slightly faster at pH 7 than at pH 8. Glycated HSA models with different degrees of glycation were built by molecular modeling. Simulated THz spectra of the models are in good agreement with the experimental data. All these show that THz spectroscopy could monitor the progression of glycation in time and that it is sensitive to reducing sugars or pH value used in the glycation process.

Study of the dielectric function of aqueous solutions of glucose and albumin by THz time-domain spectroscopy

“…It is known that a high glucose level in human blood leads to glycation of proteins [35]. Mernea with co-authors [36] have recently published the results on the use of THz timedomain spectroscopy for studying the glycation dynamics of human serum albumin in the process of its incubation with glucose and fructose for 5 - 11 weeks. However, the change in the protein structure takes place at an early stage of glycation and leads to the formation of amadori products [37].…”

Natural Aspirin-Like Compounds from White Willow (Salix alba) Bark Extract Prevent Structural Changes of Human Hemoglobin during In Vitro Non-Enzymatic Glycation and Fructation, Preserving Its Peroxidase and Esterase Activity

“…To determine the absorption in THz of human hemoglobin solutions, the protocol described by Mernea et al [7] was used and two sets of measurements were performed: without sample, when the reference spectrum was recorded (Eref (ω)) and with sample, when the spectrum of the sample was recorded (Esam (ω)); the absorption of the samples was determined by the ratio of the two measurements.…”

Terahertz spectroscopy of diabetic and non-diabetic human blood plasma pellets

“…This effect is caused by the partial replacement of free water, which strongly absorbs THz radiation, by a component that absorbs less in this frequency range, namely glucose. 12,13 This tendency was demonstrated with such objects: dry sucrose and water solutions, 14 , 15 albumin incubated with sugars (glucose or fructose), 11,16,17 glucose aqueous solution, 10 , 17,18 monosaccharide (glucose and fructose), and disaccharide (sucrose and trehalose), 10 fructose and D-glucose, 19 rat blood plasma with and without diabetes, 20,21 human blood plasma with and without diabetes, 20 and in vivo human palm skin. 22 On the other hand, the other group of authors states that the absorption coefficients and refractive index of sugar solutions increase with increasing sugar concentration.…”