Non-enzymatic glucosylation induced neo-epitopes on human serum albumin: A concentration based study

Influence of Serum Albumin on HbA1c and HbA1c-Defined Glycemic Status: A Retrospective Study

Background: Glycated hemoglobin (HbA1c) is commonly used in the diagnosis and evaluation of glycemic control in diabetes, and it may be influenced by several non-glycemic and glycemic factors, including albumin. This retrospective study investigated the influence of albumin on HbA1c and HbA1c-defined glycemic status. Methods: The demographic, hematological, and biochemical data were collected for 11,922 patients undergoing routine physical examination. Univariate and multivariate linear regression analyses, stratified analyses and interaction analyses, and multiple logistic regression were conducted to identify the association between albumin and HbA1c in people with different glycemic status. Results: HbA1c levels were inversely associated with serum albumin level (P < 0.0001) in all participants. Risk factors leading to the association included age > 45 years, high fasting plasma glucose (≥7.0 mmol/L), and anemia. The negative association between HbA1c and albumin was curved (P < 0.0001) and had a threshold effect in the HbA1c-defined diabetic population; the association was significantly stronger when the albumin level fell below 41.4 g/L (β: -0.31, 95% CI: -0.45 to -0.17, P < 0.0001). A 2 g/L increase in albumin reduced the odds of HbA1c-defined dysglycemia, diabetes, and poor glycemia control by 12% to 36%, after adjustment for all possible confounders. Conclusions: HbA1c was inversely associated with albumin level in all participants, and the association was significantly stronger in people with diabetes (defined by HbA1c criteria). For diabetic patients with lower albumin level, there was an increased risk of an erroneous HbA1c-based identification and management of glycemic status.

Determination of glycated albumin in serum and saliva by capillary electrophoresis utilizing affinity of 3-acrylamido phenylboronic acid selected by virtual screening and molecular docking

The glycated albumin (G-alb) is a potential marker of hyperglycemia in diabetes and other neurodegenerative disorders in humans. G-alb's presence in the total human serum albumin (tHSA) is an important indicator in the timely diagnosis of disease. To identify G-alb content, it needs to be isolated from non-glycated albumin (NG-alb). Here, we present Capillary electrophoresis (CE) methods with 3-acrylamido phenylboronic acid (3-APBA) as an entrapped ligand in the agarose gel to develop agarose-3-APBA functional capillary and as an affinity ligand added to the buffer without agarose. 3-APBA was selected by computational virtual screening of several phenylboronic acid (PBA) compounds and other ligands to bind G-alb and separate from NG-alb selectively. The agarose-3-APBA functional capillary method involved agarose gel dilution approach coupled with injection pressure to obtain reduced viscosity and sufficient injection volume of protein samples. The method delivered separation in 9.7 min, with a resolution of 3.4, G-alb recovery up to 65%, and took 25 min to complete the entire process. The second method involved 3-APBA as an affinity ligand in the buffer and delivered separation in 4.2 min, with a resolution of 6.4, G-alb recovery up to 102% recovery, with relatively easy procedures. Therefore, it was further applied to determine G-alb content from tHSA in human serum and saliva. The G-alb found content in serum samples was in the range of 21. 1 ± ± 1.4% to 40.5  ± 1.6% out of tHSA and 25.1  ± 1.6% to 33.3 1.4% in saliva. The binding mechanisms were investigated by molecular dockings, which revealed hydrogen bonding, π-π, and van der walls interactions between 3-APBA and G-alb. The affinity was validated by affinity capillary electrophoresis (ACE), which revealed relatively strong interactions between 3-APBA and G-alb with the binding constant (K_b) of 4.53 × 10⁹M ^- 1 to the 3.41 × 10⁸M ^- 1 of 3-APBA and NG-alb. The affinity of 3-APBA toward G-alb was increased at pH 9.0 of the borax-borate (BB) buffer as background electrolyte (BGE). The limit of detection (LOD) was 10 nM, repeatability (RSD, n = 3) ≤ 1.4%, and recovery rate was 87.8 ± 1.6 to 100 ± 1.4% in serum and 97.3 ± 1.3 to 102.6 ± 1.1% in saliva. The sensitivity and reproducibility of the method met the detection requirements.

A study on hepatopathic, dyslipidemic and immunogenic properties of fructosylated-HSA-AGE and binding of autoantibodies in sera of obese and overweight patients with fructosylated-HSA-AGE

Over consumption of fructose may lead to obesity and dyslipidemia and cause fructosylation-induced alterations in the structure and function of proteins. The aim of this study was to investigate the role of fructosylated-HSA-AGE in the pathogenesis of fatty liver (NAFLD and NASH) by biochemical, immunological and histological studies. Immunogenicity of fructosylated-HSA-AGE was probed by inducing antibodies in rabbits. Fructosylated-HSA-AGE was found to be highly immunogenic. Furthermore, fructosylated-HSA-AGE caused mild fibrosis with steatosis and portal inflammation of hepatocytes in experimental animals. Liver function test and dyslipidemic parameters in immunized animals were also found to be raised. Ultrasonography, which should form part of the assessment of chronically raised transaminases, shows fatty infiltration. Interestingly, alanine aminotransferase (ALT), aspartate aminotransferase (AST), bilirubin, total cholesterol (TC) and triglyceride (TG) profiles confirms USG images of overweight, obese patients. Thus, present study demonstrates that fructosylated-HSA-AGE is hepatotoxic, immunologically active and may cause dyslipidemia.

Nitroxidized-Albumin Advanced Glycation End Product and Rheumatoid Arthritis

Rheumatoid arthritis (RA) is an autoimmune disease whose major clinical consequence is inflammation of small joints and contiguous structures. Oxidative and nitrosative stress along with increased formation of advanced glycation end products (AGEs) play an important role in the disease process. Generation of reactive species during glycation of proteins further adds to the oxidative and nitrosative stress. Albumin, being the most abundant plasma protein, is frequently targeted by different oxidizing and nitrating agents, including peroxynitrite (OONO-) anion. Albumin is also targeted and modified by dicarbonyl metabolites (glyoxal and methylglyoxal) which are formed in oxidative and non-oxidative processes during the synthesis of AGEs. The endogenously formed OONO- and dicarbonyls may modify plasma albumin including those albumin that have travelled or migrated to synovial cells and caused nitration, oxidation, and glycation. These modifications may produce crosslinks, aggregate in albumin and confer immunogenicity. Simultaneous modification of albumin by OONO- and dicarbonyls may generate nitroxidized-AGE-albumin which may persist in circulation for a longer duration compared to native albumin. Nitroxidized-AGE-albumin level (or serum autoantibodies against nitroxidized- AGE-albumin) along with other pre-clinical features may help predict the likely onset of RA.

Nonenzymatic glycosylation of human serum albumin and its effect on antibodies profile in patients with diabetes mellitus

Background

Albumin glycation and subsequent formation of advanced glycation end products (AGEs) correlate with diabetes and associated complications.

Methods

Human Serum Albumin (HSA) was modified with D-glucose for a 40 day period under sterile conditions at 37°C. Modified samples along with native HSA (unmodified) were analyzed for structural modifications by UV and fluorescence, FTIR, Liquid chromatography mass spectrometry (LCMS) and X–ray crystallography. New-Zealand white female rabbits immunized with AGEs, represent auto-antibodies formation as assessed by competitive and direct binding enzyme-linked immunosorbent assay (ELISA). Neo-epitopesagainst In-vitro formed AGEs were characterized in patients with diabetes mellitus type 2 (n = 50), type 1 (n = 50), gestational diabetes (n = 50) and type 2 with chronic kidney disease (CKD) with eGFR level 60–89 mL/min (n = 50) from serum direct binding ELISA.

Results

Glycated-HSA showed amarked increase in hyperchromicity of 65.82%,71.98%, 73.62% and 76.63% at λ_{280 nm} along with anincreasein fluorescence intensity of 65.82%, 71.98%, 73.62% and 76.63% in glycated-HSA compared to native. FTIR results showed theshifting of Amide I peak from 1656 cm^_1 to 1659 cm^_1 and Amide II peak from 1554 cm^_1 to 1564 cm^_1 in glycated-HSA, with anew peak appearance of carbonyl group at 1737 cm-1. LCMS chromatogram of glycated-HSA showed thepresence of carboxymethyl lysine (CML) at 279.1 m/z. Immunological analysis showed high antibody titre>1:12,800 in theserum of rabbits immunized with glycated-HSA (modified with 400 mg/dL glucose) and inhibition of 84.65% at anantigen concentration of 20μg/mL. Maximum serum auto-antibody titre was found in T2DM (0.517±0.086), T1DM (0.108±0.092), GDM (0.611±0.041) and T2DM+CKD (0.096±0.25) patients immunized with glycated-HSA (modified with 400 mg/dL glucose).

Conclusions

Non-enzymatic glycosylation of HSA manifests immunological complications in diabetes mellitus due to change in its structure that enhances neo-epitopes generation.