Chromatographic analysis of the effects of fatty acids and glycation on binding by probes for Sudlow sites I and II to human serum albumin

Enantioselective Human Serum Albumin Binding of Apremilast: Liquid Chromatographic, Fluorescence and Molecular Docking Study

The interaction between human serum albumin (HSA) and apremilast (APR), a novel antipsoriatic drug, was characterized by multimodal analytical techniques including high-performance liquid chromatography (HPLC), fluorescence spectroscopy and molecular docking for the first time. Using an HSA chiral stationary phase, the APR enantiomers were well separated, indicating enantioselective binding between the protein and the analytes. The influence of chromatographic parameters-type and concentration of the organic modifier, buffer type, pH, ionic strength of the mobile phase, flow rate and column temperature-on the chromatographic responses (retention factor and selectivity) was analyzed in detail. The results revealed that the eutomer S-APR bound to the protein to a greater extent than the antipode. The classical van 't Hoff method was applied for thermodynamic analysis, which indicated that the enantioseparation was enthalpy-controlled. The stability constants of the protein-enantiomer complexes, determined by fluorescence spectroscopy, were in accordance with the elution order observed in HPLC (K_R-APR-HSA = 6.45 × 10³ M^-1, K_S-APR-HSA = 1.04 × 10⁴ M^-1), showing that, indeed, the later-eluting S-APR displayed a stronger binding with HSA. Molecular docking was applied to study and analyze the interactions between HSA and the APR enantiomers at the atomic level. It was revealed that the most favored APR binding occurred at the border between domains I and II of HSA, and secondary interactions were responsible for the different binding strengths of the enantiomers.

Systematic interaction of plasma albumin with the efficacy of chemotherapeutic drugs

Albumin, as the most abundant plasma protein, plays an integral role in the transport of a variety of exogenous and endogenous ligands in the bloodstream and extravascular spaces. For exogenous drugs, especially chemotherapeutic drugs, binding to and being delivered by albumin can significantly affect their efficacy. Meanwhile, albumin can also bind to many endogenous ligands, such as fatty acids, with important physiological significance that can affect tumor proliferation and metabolism. In this review, we summarize how albumin with unique properties affects chemotherapeutic drugs efficacy from the aspects of drug outcome in blood, toxicity, tumor accumulation and direct or indirect interactions with fatty acids, plus application of albumin-based carriers for anti-tumor drug delivery.

Application of a stepwise frontal analysis method in cell membrane chromatography

Bio-affinity chromatography is used in the study of drug-receptor interactions. A stepwise frontal analysis (SFA) method was developed based on frontal analysis (FA). A high expression alpha 1A adrenergic receptor (α_1A AR) cell membrane chromatography (CMC) method was then developed and combined with SFA to investigate the affinity of three model α_1A AR-binding drugs towards α_1A AR. Equilibrium dissociation constant (K_d) values for drug-receptor interactions were determined by FA and SFA; results showed that these methods were highly consistent. The results demonstrate that the CMC/SFA method is a time-saving and less wasteful method than traditional method for the evaluation of drug-receptor binding characteristics, and could be used to study the interactions between drugs and membrane receptors.

Ligand binding to natural and modified human serum albumin

This paper reports evaluation of ligand binding constants for unmodified or biotinylated HSA (HSA_B) for two well-known HSA binding ligands, naproxen and bromocresol green. Results demonstrate differential scanning calorimetry (DSC) is a reliable quantitative method for straight-forward and rapid evaluation of ligand binding constants for HSA and modified derivatives. DSC measured the thermodynamic stability of free and ligand-bound HSA and HSA_B at pH = 6.0, 7.4 and 8.0. DSC analysis provided a quantitative gauge of responses of HSA and HSA_B thermodynamic stability to ligand binding. The influence of different levels of biotinylation of HSA_B on ligand binding, and how ligand binding varied as a function of pH for these molecules was also examined. In the three pH environments, biotinylation increased stability of HSA_B alone compared to free HSA at pH 7.4. Stabilities of free protein and ligand-bound complexes varied with pH in the order, pH = 6.0>7.4>8.0. Our analytical approach provided very accurate estimates for known binding constants of these ligands for HSA. Results revealed, for both ligands, extent of biotinylation of HSA_B affected binding, reducing binding constants from three to 100-fold. DSC analysis was able to delineate inter-relationships between molecular structure and thermodynamic stability of HSA and HSA_B bound by ligands; and their variations with pH.

Serum Levels and Removal by Haemodialysis and Haemodiafiltration of Tryptophan-Derived Uremic Toxins in ESKD Patients

Tryptophan is an essential dietary amino acid that originates uremic toxins that contribute to end-stage kidney disease (ESKD) patient outcomes. We evaluated serum levels and removal during haemodialysis and haemodiafiltration of tryptophan and tryptophan-derived uremic toxins, indoxyl sulfate (IS) and indole acetic acid (IAA), in ESKD patients in different dialysis treatment settings. This prospective multicentre study in four European dialysis centres enrolled 78 patients with ESKD. Blood and spent dialysate samples obtained during dialysis were analysed with high-performance liquid chromatography to assess uremic solutes, their reduction ratio (RR) and total removed solute (TRS). Mean free serum tryptophan and IS concentrations increased, and concentration of IAA decreased over pre-dialysis levels (67%, 49%, −0.8%, respectively) during the first hour of dialysis. While mean serum total urea, IS and IAA concentrations decreased during dialysis (−72%, −39%, −43%, respectively), serum tryptophan levels increased, resulting in negative RR (−8%) towards the end of the dialysis session (p < 0.001), despite remarkable Trp losses in dialysate. RR and TRS values based on serum (total, free) and dialysate solute concentrations were lower for conventional low-flux dialysis (p < 0.001). High-efficiency haemodiafiltration resulted in 80% higher Trp losses than conventional low-flux dialysis, despite similar neutral Trp RR values. In conclusion, serum Trp concentrations and RR behave differently from uremic solutes IS, IAA and urea and Trp RR did not reflect dialysis Trp losses. Conventional low-flux dialysis may not adequately clear Trp-related uremic toxins while high efficiency haemodiafiltration increased Trp losses.

Analysis of the Binding of Aripiprazole to Human Serum Albumin: The Importance of a Chloro-Group in the Chemical Structure

Aripiprazole (ARP), a quinolinone derivative, is an atypical antipsychotic drug that is used in the treatment of schizophrenia. ARP has an extensive distribution and more than 99% of the ARP and dehydro-ARP, the main active metabolite, is bound to plasma proteins. However, information regarding the protein binding of ARP is limited. In this study, we report on a systematic study of the protein binding of ARP. The interaction of ARP and structurally related compounds with human serum albumin (HSA) was examined using equilibrium dialysis, circular dichroism (CD) spectroscopy, fluorescent probe displacement, and an X-ray crystallographic analysis. The binding affinities (nK) for ARP and its main metabolite, dehydro-ARP with HSA were found to be significantly higher than other structurally related compounds. The results of equilibrium dialysis experiments and CD spectral data indicated that the chloro-group linked to the phenylpiperazine ring in the ARP molecule plays a major role in the binding of these ligands to HSA. Furthermore, fluorescent probe displacement results indicated that ARP appears to bind at the site II pocket in subdomain III. A detailed CD spectral analysis suggests that the chloro-group linked to the phenylpiperazine ring may control the geometry of the ARP molecule when binding in the site II binding pocket. X-ray crystallographic analysis of the ARP-HSA complex revealed that the distance between the chlorine atom at the 3-positon of dichlorophenyl-piperazine on ARP and the sulfur atom of Cys392 in HSA was 3.4-3.6 Å. A similar halogen bond interaction has also been observed in the HSA structure complexed with diazepam, which also contains a chloro-group. Thus, the mechanism responsible for the binding of ARP to a protein elucidated here should be relevant for assessing the pharmacokinetics and pharmacodynamics of ARP in various clinical situations and for designing new drugs.

Rapid Investigation and Screening of Bioactive Components in Simo Decoction via LC-Q-TOF-MS and UF-HPLC-MD Methods

Simo decoction (SMD), as a traditional medicine, is widely used in the treatment of gastrointestinal dysmotility in China. In this study, a combined method of liquid chromatography quadrupole time-of-flight mass spectrometry (LC-Q-TOF-MS) and ultrafiltration high-performance liquid chromatography molecular docking (UF-HPLC-MD) was efficiently employed to identify and screen bioactive ingredients in SMD. Ninety-four major constituents were identified or tentatively characterized by comparing their retention times and mass spectra with standards or literature data by using LC-Q-TOF-MS, and the ascription of those compounds were classified for the first time. Among them, 13 bioactive ingredients, including norisoboldine, eriocitrin, neoeriocitrin, narirutin, hesperidin, naringin, neohesperidin, hesperitin-7-O-glucoside, linderane, poncirin, costunolide, nobiletin, and tangeretin, were primarily identified as the human serum albumin (HSA) ligands at a range of docking scores from −29.7 to −40.6 kJ/mol by UF-HPLC-MD. The results indicate the systematic identification and screening of HSA ligands from Simo decoction guided by LC-Q-TOF-MS and UF-HPLC-MD represents a feasible and efficient method that could be extended for the identification and screening of other bioactive ingredients from natural medicines.

Glycation of human serum albumin impairs binding to the glucagon-like peptide-1 analogue liraglutide

The long-acting glucagon-like peptide-1 analogue liraglutide has proven efficiency in the management of type 2 diabetes and also has beneficial effects on cardiovascular diseases. Liraglutide's protracted action highly depends on its capacity to bind to albumin via its palmitic acid part. However, in diabetes, albumin can undergo glycation, resulting in impaired drug binding. Our objective in this study was to assess the impact of human serum albumin (HSA) glycation on liraglutide affinity. Using fluorine labeling of the drug and ¹⁹F NMR, we determined HSA affinity for liraglutide in two glycated albumin models. We either glycated HSA in vitro by incubation with glucose (G25- or G100-HSA) or methylglyoxal (MGO-HSA) or purified in vivo glycated HSA from the plasma of diabetic patients with poor glycemic control. Nonglycated commercial HSA (G0-HSA) and HSA purified from plasma of healthy individuals served as controls. We found that glycation decreases affinity for liraglutide by 7-fold for G100-HSA and by 5-fold for MGO-HSA compared with G0-HSA. A similarly reduced affinity was observed for HSA purified from diabetic individuals compared with HSA from healthy individuals. Our results reveal that glycation significantly impairs HSA affinity to liraglutide and confirm that glycation contributes to liraglutide's variable therapeutic efficiency, depending on diabetes stage. Because diabetes is a progressive disease, the effect of glycated albumin on liraglutide affinity found here is important to consider when diabetes is managed with this drug.

Fabrication of size-controlled linoleic acid particles and evaluation of their in-vitro lipotoxicity

The biological activities of fatty acids (FAs) can differ with size even for lipids of similar compositions. The aim of this study was to develop size-controlled FA particles and to evaluate their toxicity as a function of size. Well-stabilized nano- and microscale linoleic acid (LA) were fabricated based on specific physical factors. Then, resulting LAs were characterized by size distribution, surface charge, assembly structure, composition, and serum effects. The sizes of the nano- (LA_nano) and microscale (LA_micro) LAs, determined by electron microscopy, were 109 nm and 12 μm, respectively. LA_nano, a multilamellar structure as determined by cryo-electron microscopy, was rapidly internalized into cells via free fatty acid receptor 3. After internalization, LA_nano, but not LA_micro, induced nuclear translocation of fatty acid binding protein 4 (FABP4). Translocation of FABP4 into the nucleus then induced expression of the FA metabolism-related genes InsR and AdipoR1. Their expression was significantly increased in the presence of only LA_nano. Cytotoxicity was also significantly increased in cells treated with LA_nano, but not LA_micro, as indicated by the endoplasmic reticulum stress markers CHOP and GRP78. Therefore, our results demonstrated that FAs with the same composition but varying in size can cause different cellular responses.