Activity Of Human Serum Albumin Research Articles

Exploring the binding mechanism and esterase-like activity of human serum albumin with levofloxacin and its choline based conjugates: A biophysical approach

Human serum albumin (HSA) effectively binds to compounds having different molecular weight and thus facilitates their distribution in the living organisms. Thus, the binding interactions between a potential antibacterial drug (levofloxacin) and synthesized choline based levofloxacinate conjugates with HSA have been explored. The binding efficacy and mechanism were explored by utilizing different spectroscopic techniques; UV–Visible, steady state fluorescence, time resolved fluorescence and esterase-like activity. The interactions between the ligands and protein were electrostatic as well as hydrophobic in nature. The influence of different ligands having different alkyl chain shows quenching of the fluorescence emission of HSA. The spontaneous binding/quenching of HSA with ligands was static in nature, validated by steady state and time resolved fluorescence spectroscopy. Also, the impact of these ligands on the conformation of the native HSA structure was evaluated by using circular dichroism spectroscopy. In combination to the structural change study, the native protein functionality was observed (in terms of ‘esterase-like activity’) which has been found to be on lower side due to ligand binding. Further, we have performed the reverse study to check the impact of HSA on the fluorescent fluoroquinolone drug. The current study may prove helpful in elucidating the chemico-biological interactions which may prove useful in the pharmaceuticals, pharmacology, and different biochemistry fields.

Albumin Is a Component of the Esterase Status of Human Blood Plasma.

The esterase status of blood plasma can claim to be one of the universal markers of various diseases; therefore, it deserves attention when searching for markers of the severity of COVID-19 and other infectious and non-infectious pathologies. When analyzing the esterase status of blood plasma, the esterase activity of serum albumin, which is the major protein in the blood of mammals, should not be ignored. The purpose of this study is to expand understanding of the esterase status of blood plasma and to evaluate the relationship of the esterase status, which includes information on the amount and enzymatic activity of human serum albumin (HSA), with other biochemical parameters of human blood, using the example of surviving and deceased patients with confirmed COVID-19. In experiments in vitro and in silico, the activity of human plasma and pure HSA towards various substrates was studied, and the effect of various inhibitors on this activity was tested. Then, a comparative analysis of the esterase status and a number of basic biochemical parameters of the blood plasma of healthy subjects and patients with confirmed COVID-19 was performed. Statistically significant differences have been found in esterase status and biochemical indices (including albumin levels) between healthy subjects and patients with COVID-19, as well as between surviving and deceased patients. Additional evidence has been obtained for the importance of albumin as a diagnostic marker. Of particular interest is a new index, [Urea] × [MDA] × 1000/(BChEb × [ALB]), which in the group of deceased patients was 10 times higher than in the group of survivors and 26 times higher than the value in the group of apparently healthy elderly subjects.

Nanoplastics alter the conformation and activity of human serum albumin

Nanoplastics finds its presence in most of the consumer products. Their chance of coming in contact with human cells and components is rampant. This study focuses on the interaction of polystyrene nanoplastics (PSNPs) with human serum albumin (HSA), ultimately causing structural and functional properties of the protein. Fluorescence and UV–Visible spectroscopic studies reported that PSNPs form a spontaneous ground-state complex with HSA, by hydrogen bonding, van der waal's, and hydrophobic force of attraction. This causes changes in the environment around major aromatic amino acids, especially tryptophan-214, which has a strong affinity with PSNPs. Further docking analysis confirmed hydrophobic interactions between PSNPs and aromatic amino acids in subdomain IIA of HSA. A shift in amide bands in HSA, as determined by FTIR analysis confirmed the disturbances in its secondary structure followed by reordering which will lead to the unfolding of HSA. Besides, PSNPs reduce the esterase activity of HSA by competitive inhibition. This molecular-level information such as binding energy, binding site, binding forces, reversible or irreversible binding, and structural changes of protein will shed light on the extent of toxicity in humans. This study will emphasize the urgent need for regulation of the use of nanoplastics (NPs) in consumer products, as well as the need for more research to determine the fate of NPs in the biological system.

The effects of synthesized silver nanowires on the structure and esterase-like activity of human serum albumin and their impacts on human endometrial stem cells

Silver nanowires (AgNWs) were synthesized and fabricated then their effects on the structure and esterase-like activity of Human Serum Albumin (HSA) were evaluated in vitro. Afterward, their impacts on the growth of human endometrial stem cells (hEnSCs) were studied. The results showed that AgNWs could form a complex with HSA and did not affect the secondary structure of HSA only at lower concentrations. The binding constant for the AgNWs-HSA complex was found to be 1.4 × 104 M−1. The distance between HSA and AgNWs was acquired according to the Förster theory. The value of ΔG ° displayed that AgNWs interact with HSA and the hydrophobic force plays a major role in this interaction. HSA lost its esterase-like activity at a higher concentration of AgNWs. Cell viability assays indicated that AgNWs were toxic toward hEnSCs at higher concentrations. This study demonstrated that AgNWs can be utilized in nanotechnology-based bio-applications only at lower concentrations.

Probing the effects of synthesized silver nanowire/reduced graphene oxide composites on the structure and esterase-like activity of human serum albumin and its impacts on human endometrial stem cells: A new platform in nanomedicine

Objective(s): Nowadays, the unique and fascinating properties of graphene‐based nanocomposites make them one of the most promising materials for therapeutics, delivery carriers as well as tissue engineering. On the other hand, silver nanowire has been attracting more attention in nanomedicine applications, too. In this study, the effects of synthesized silver nanowire/reduced graphene oxide (AgNWs/rGO) composites on the structure and esterase-like activity of Human Serum Albumin (HSA), as well as its impacts on Human Endometrial Stem Cells (hEnSCs), were evaluatedMaterials and Methods: AgNWs/rGO composite was first synthesized and fabricated. Subsequently, its effects on the structure and esterase-like activity of HSA were evaluated by UV-Visible spectroscopy, circular dichroism spectroscopy, and fluorescence spectroscopy. Afterward, its impacts on the viability and growth of hEnSCs were studied by MTT assay, DAPI staining, and flow cytometry analysis.Results: The spectroscopic results showed that AgNWs/rGO composite could form a complex with HSA, however, did not affect the secondary structure of HSA and the binding constant for this complex was found to be 5.4×104 mL.mg-1. Furthermore, HSA maintained most of its activity in the presence of the AgNWs/rGO composite. Based on FRET (fluorescence resonance energy transfer) data the value of r0 was less than 7 nm signifying that the energy transfer from HSA to AgNWs/rGO composite occurs with a high level of possibility. The MTT assay, DAPI staining, and flow cytometry analysis indicated that the AgNWs/rGO composite was non-toxic towards hEnSCs. Conclusion: Our results suggest that the prepared AgNWs/rGO composite, potentially, is suitable in nanomedicine applications such as tissue engineering and drug delivery.

Study on the binding mechanism of thiamethoxam with three model proteins:spectroscopic studies and theoretical simulations

As a top-selling neonicotinoid insecticide widely used in the field, thiamethoxam is an environmental pollutant because of the accumulation in ecosystem and has also been reported that it has potential risks to the health of mammals even humans. In order to understand the binding mechanism of thiamethoxam with biological receptors, spectroscopic techniques and theoretical simulations was used to explore the specific interactions between thiamethoxam and proteins. Interestingly, the results indicated that hydrophobic interaction as the main driving force, thiamethoxam formed a single binding site complex with proteins spontaneously, resulting in a decrease in the esterase-like activity of human serum albumin. The results of computer simulation showed that there were hydrophobic, electrostatic and hydrogen bonding interactions between thiamethoxam and receptors. The results of experiment and computer simulation were mutually confirmed, so a model was established for the interaction between the two which uncovered the structural characteristics of the binding site. This research provided new insights for the structure optimization of thiamethoxam, as well as gave an effective reference for evaluating the risk of thiamethoxam systemically in the future.

Z-Acrylonitrile Derivatives: Improved Synthesis, X-ray Structure, and Interaction with Human Serum Albumin.

In the synthesis of heterocyclic compounds, acrylonitrile derivatives are the most important and appropriate precursors. These compounds are the most important intermediates and subunits for the enhancement of molecules having pharmaceutical or biological interests. Nitrogen-containing compounds have received extensive consideration in the literature over the years. A facile, economic and efficient method has been developed for the synthesis of acrylonitrile derivatives using p-nitrophenylacetonitrile and aromatic/heterocyclic aldehydes in the presence of zinc chloride at room temperature. Spectroscopic data were obtained using the following instruments: Fourier transform infrared spectra (KBr discs, 4000-400 cm-1) by Shimadzu IR-408 Perkin-Elmer 1800 instrument; 1H NMR and 13C NMR spectra by Bruker Avance-II 400 MHz using DMSO-d6 as a solvent containing TMS as the internal standard. To continue our ongoing studies to synthesize heterocyclic and pharmaceutical compounds by mild, facile and efficient protocols, herein we wish to report our experimental results on the synthesis of acrylonitrile derivatives, using various aromatic/heterocyclic aldehydes and p-nitrophenylacetonitrile in the presence of zinc chloride in ethanolic media at room temperature. Some of the new compounds were tested for their human serum albumin activity (HSA) while a study of interaction with HSA protein was performed for compounds 3a and 3b. The results show that compound 3b binds tightly to HSA as compared to compound 3a. It can be concluded that acrylonitrile derivatives can be synthesized by an efficient method via the reaction of p-nitrophenylacetonitrile with aromatic/heterocyclic aldehydes by the use of zinc chloride as an effective solid catalyst. The remarkable features of this procedure include excellent yields (90-95%), short reaction period (30 min.), moderate reaction environment, easy workup procedure and managing of the catalyst. This method may find a wide significance in organic synthesis for the synthesis of the Z-acrylonitrile.

Interaction of novel Aurora kinase inhibitor MK-0457 with human serum albumin: Insights into the dynamic behavior, binding mechanism, conformation and esterase activity of human serum albumin

MK-0457, a new pan-aurora kinase inhibitor, is in Phase II clinical development for the treatment of multiple tumor types and hematologic malignancies. The present work explored the dynamic behaviors and interaction mechanism of MK-0457 to human serum albumin (HSA) and the effect on the esterase-like activity and conformation of HSA by computer simulations and experiments. Docking and molecular dynamics trajectory analysis indicated that MK-0457 stably bound to Sudlow’s site 2 of HSA by multiple types of interaction forces. Competitive experiments further verified MK-0457 was bound at first to Sudlow’s site 2 and then the excess of drug was bound to Sudlow’s site 1. The steady-state fluorescence combined with ultraviolet–visible absorption and fluorescence lifetime measurements specified a static quenching mechanism with association constants of 104 M−1 reflecting moderate binding affinity of MK-0457 for HSA. The analysis of Rg values showed that the structure of HSA became loose due to MK-0457 binding, inducing slight conformational changes of HSA, which was consistent with the results obtained from circular dichroism, synchronous, and 3D fluorescence spectroscopy. The esterase-like activity of HSA showed that MK-0457 inhibits the catalytic activity of subdomain IIIA of HSA by binding to the vital residues TYR411. Atomic force microscopy images indicated that MK-0457 affects the molecular sizes of HSA by transforming the morphology of HSA from aggregation diploids to small monomers. This study is beneficial for understanding the biological action of MK-0457, providing additional information about the feasibility of its transport and accumulation in blood plasma.

Effect of negative functionalisation of gold nanorods on conformation and activity of human serum albumin

The theranostic applications of gold nanorods (AuNRs) are limited due to the presence of cytotoxic cetrimonium bromide (CTAB) stabiliser, leading to the instigation of alternate stabilisers like negatively charged polystyrene sulphonate (PSS). Despite previous reports suggesting the impact of PSS-AuNRs on cells, their effect on the most abundant protein in plasma, i.e. human serum albumin (HSA), has not been studied before. Hence, the impact of PSS-AuNRs on HSA was thoroughly examined using varied spectroscopic techniques. The absorbance and fluorescence spectroscopic findings suggested the extent of ground-state complexation and tryptophan domain disruptions of HSA for different AuNR concentrations, which were also suggested based on size measurements and activation energy calculations for complex formation. Modifications in the hydrophobic environment of HSA were evaluated using synchronous fluorescence, whereas the secondary structural damages were explained using circular dichroism (CD) and FTIR analyses. Additional studies to analyse protein denaturation, fibrillation, esterase activity, and free thiol were carried out to understand structural and functional changes. The study suggested that PSS-AuNRs showed concentration-dependent alterations in HSA structure, but the extent of protein toxicity was considerably lesser for PSS-AuNRs of similar dimensions compared to the data available for CTAB-AuNRs; thus, highlighting that PSS-AuNRs could be safer for biomedical applications.

Effect of cationic gemini surfactant and its monomeric counterpart on the conformational stability and esterase activity of human serum albumin

The binding effect of gemini surfactant, hexanediyl-α,ω-bis-(N-(2-hydroxyethyl)–N-methylhexadecylammonium bromide) (16-6-16 MEA) and its monomeric counterpart N-(2-hyroxyethyl)-N,N-dimethylhexadecylammonium bromide (16-MEA) on the structure and esterase like activity of human serum albumin (HSA) was unravelled by using UV–visible, fluorescence, three dimensional fluorescence, time resolved fluorescence and circular dichroism techniques in combination with molecular docking and molecular dynamic simulation methods. Fluorescence quenching mechanism was employed to estimate the Stern–Volmer quenching constants, Ksv, and the corresponding thermodynamic parameters like ∆G, ∆S and ∆H for HSA-16 MEA/16-6-16 MEA systems. The results showed the static quenching mechanism and spontaneous binding of 16 MEA/16-6-16 MEA with HSA. In addition to other interactions, the hydrophobic interaction (which is more effective in case gemini surfactant) plays major role in the process of binding of both the surfactants with HSA. Synchronous fluorescence reveals that there is a slight effect of 16 MEA/16-6-16 MEA on the fluorescence intensity of tyrosine but a significant effect on tryptophan. UV–visible results obtained, suggest the complex formation between HSA and 16MEA/16-6-16 MEA through static quenching mechanism. Circular dichroism results confirmed that the decrease in the α-helical content of HSA is more on interaction with 16-6-16 MEA as compared to 16 MEA. In addition, the esterase activity of HSA was also done, which was found to decrease in presence of both 16 MEA and 16-6-16 MEA. Additionally, we also utilized computational approaches for deep insight into the binding of 16 MEA/16-6-16 MEA with HSA and the results well matched with our experimental results.

Exploring the interaction between picoplatin and human serum albumin: The effects on protein structure and activity

For the first time, the effects of picoplatin on the structure and esterase-like catalytic activity of human serum albumin (HSA) have been investigated by spectroscopic approaches and molecular modeling. The circular dichroism (CD) spectral examinations indicated that the binding of picoplatin with HSA induced a slight decrease of a-helix content of protein and unfolded the constituent polypeptides of the protein. The synchronous fluorescence and three-dimensional fluorescence spectral methods were used to estimate the effect of picoplatin on the micro-environmental changes of the Trp and Tyr residues of HSA, indicating that the micro-environment around the Tyr and Trp residue is partly disturbed by picoplatin. UV–vis absorption spectral result indicated the formation of the ground state complex between picoplatin with HSA. The ANS binding assay indicated the existence of competitive combination of picoplatin and ANS with HSA. The studies on the effects of picoplatin on the binding of HSA with bilirubin and heme showed that picoplatin binding caused a change of angle between two chromophores of bound bilirubin and the binding site of picoplatin does not locate in subdomain IB in HSA that bound with heme. The molecular modeling results showed that picoplatin binds to the connection between domain I and domain II by hydrophobic, hydrogen bonds, and van der Waals forces. In addition, HSA maintains most of its esterase activity in the presence of picoplatin. The investigations on how picoplatin interacts with HSA are important for the understanding of the anticancer mechanism and toxicity of platinum-based anticancer drug.

Insights into the effect of N-acetyl-L-cysteine-capped CdTe quantum dots on the structure and activity of human serum albumin by spectroscopic techniques

Quantum dots (QDs) are a kind of nanostructured semiconductor crystals with the size range of 1–10nm. Their unique photophysical properties and potential toxicity to human health have aroused wide concern of scientists and general public. However, the interaction mechanism of QDs on human serum albumin (HSA, the vital protein in human blood) from both structural and functional perspectives is rarely reported. In the present work, effects of N-acetyl-L-cysteine-capped CdTe quantum dots with fluorescence emission peak at 612nm (QDs-612) on the conformation and function of HSA were investigated by spectroscopic methods, molecular docking study and esterase activity assay. The hydrophobic interaction between HSA and QDs-612 was spontaneous with the binding constants calculated to be 6.85×105Lmol−1 (298K) and 8.89×105Lmol−1 (308K). The binding of QDs-612 to HSA induced the static quenching of fluorescence and the changes of secondary structure and microenvironment of Tyr-411 residue, which resulted in serious decrease on the hydrolysis of substrate p-nitrophenylacetate in esterase activity assay of HSA. This work confirms the possibility on direct interaction of QDs-612 with HSA and obtains a possible mechanism of relationship between conformation and function of HSA.

Amino acids of importance for the antioxidant activity of human serum albumin as revealed by recombinant mutants and genetic variants.

To determine molecular information about the antioxidant properties of human serum albumin, which is an important extracellular antioxidant. To obtain this information, we studied this function of the protein by using H2O2 as the representative reactive oxygen species and two recombinant mutants and ten genetic variants with single-residue mutations. The antioxidant capabilities of the isoforms were registered as their ability to diminish the H2O2-induced conversion of dihydrorhodamine 123 to rhodamine 123, which can emit fluorescence at 536 nm. Structural properties were examined by circular dichroism and SDS-PAGE. Cysteine residues are important for the antioxidant function, but their effect depends on their position in the protein, with Cys410 > Cys34 ~ Cys169 (when not involved in forming a disulfide bond). Likewise, the substitution of a glutamic acid at position 122 or 541, but not at 240 or 560, improves the antioxidant effect, perhaps by making the methionine residues in their vicinity, Met123 and Met548, respectively, more accessible for the oxidant. A lysine at position 505, but not at 82 or 570, decreases the oxidative effect. Finally, the mutations D269G and K276N had no effect. In certain cases, albumin acts as a sacrificial antioxidant, as in the case of the mutants C34S and, in particular, R410C and E505K. The information gained is of protein chemical relevance, but it may also be helpful in understanding the function of proteins that act as antioxidants in biological systems subjected to oxidative stress in conditions such as inflammation and aging.

Superoxide Dismutase Activity of the Naturally Occurring Human Serum Albumin–Copper Complex without Hydroxyl Radical Formation

The superoxide radical anion (O2(.-)) is biologically toxic and contributes to the pathogenesis of various diseases. Here we describe the superoxide dismutase (SOD) activity of human serum albumin (HSA) complexed with a single Cu(II) ion at the N-terminal end (HSA-Cu complex). The structure of this naturally occurring copper-coordinated blood serum protein has been characterized by several physicochemical measurements. The O2(.-) dismutation ability of the HSA-Cu (1:1) complex is almost the same as that of the well-known SOD mimics, such as Mn(III) -tetrakis(N-methylpyridinium)porphyrin. Interestingly, the HSA-Cu complex does not induce a subsequent Fenton reaction to produce the hydroxyl radical (OH(.)), which is one of the most harmful reactive oxygen species.

Gold Nanoparticle Inclusion into Protein Nanotube as a Layered Wall Component

We describe the synthesis, structure, and catalytic activity of human serum albumin (HSA) nanotubes (NTs) including gold nanoparticles (AuNPs) as a layered wall component. The NTs were fabricated as an alternating layer-by-layer assembly of AuNP and HSA admixture (a negatively charged part) and poly-l-arginine (PLA, a positively charged part) into a track-etched polycarbonate membrane (400 nm pore diameter) with subsequent dissolution of the template. SEM images showed the formation of uniform hollow cylinders of (PLA/AuNP-HSA)3 with a 426 ± 12 nm outer diameter and 65 ± 7 nm wall thickness. Transmission electron microscopy and energy dispersive X-ray measurements revealed high loading of AuNPs in the tubular wall. HSAs bind strongly onto the individual AuNP (K = 1.25 × 10(9) M(-1)), generating a core-shell AuNP-HSA corona, which is the requirement of the robust NT formation. Calcination of the (PLA/AuNP-HSA)3 NTs at 500 °C under air yielded red solid NTs composed of thermally fused AuNPs. From the mass decrease by heat treatment, we calculated the weight of the organic components (PLA and HSA) and thereby constructed a six-layer model of the tube. The (PLA/AuNP-HSA)3 NTs serve as a heterogeneous catalyst for reduction of 4-nitrophenol with sodium borohydrate. Furthermore, implantation of the stiff (PLA/AuNP-HSA)3 NTs vertically onto glass plate produced uniformly cylindrical tube arrays.

Insignificant β-lactamase activity of human serum albumin: no panic to nonmicrobial-based drug resistance

Recently, it was speculated that human serum albumin (HSA) possesses β-lactamase activity and could contribute to nonmicrobial-based antibiotic resistance, owing to its ability to hydrolyse the β-lactam ring of nitrocefin. Moreover, the putative β-lactamase activity of HSA has been shown to increase significantly in the presence of environmental pollutants (1-naphthol and 2-naphthol). It was postulated that HSA could also cleave the β-lactam ring of clinically significant antibiotics. We studied the β-lactamase activity of HSA on clinically significant antibiotics of cephalosporin group in the presence of environmental pollutants by determining specific activity, enzyme kinetics and minimum inhibitory concentrations (MIC). The specific activity of HSA on various cephalosporins was found to be 1181-34550 times lower than that observed for recombinant CTX-M-15 (used as positive control). The catalytic efficiency (kcat /Km ) of HSA on nitrocefin hydrolysis was 126·7 times lower than that of recombinant CTX-M-15, and it has increased only 2- to 3-folds in the presence of environmental pollutants. Moreover, cephalosporins were not hydrolysed by HSA under experimental conditions. The MIC data also showed that HSA is incapable of hydrolysing cephalosporins. The study concludes that HSA is inefficient to cleave antibiotics of cephalosporin group and hence does not contribute to nonmicrobial-based antibiotic resistance. Earlier reports showed that human serum albumin (HSA) possesses β-lactamase activity, owing to its ability to cleave nitrocefin, and thus contributes to antibiotic resistance. Also, its β-lactamase activity is augmented when exposed to pollutants. As nitrocefin is not an antibiotic of clinical use, the conclusion drawn does not represent a true scenario and is misleading. Our results showed that HSA is inefficient in cleaving nitrocefin as compared to a true β-lactamase (CTX-M-15) and is practically inactive on cephalosporin antibiotics even in the presence pollutants. The findings showed that HSA-mediated hydrolysis of β-lactam antibiotics does not contribute to antibiotic resistance.

Quantitative evaluation of the role of cysteine and methionine residues in the antioxidant activity of human serum albumin using recombinant mutants

The importance of cysteine (Cys) and methionine (Met) residues for the antioxidant activity of human serum albumin (HSA) was investigated using recombinant HSA mutants, in which Cys34 and/or the six Met residues had been mutated to Ala. The scavenging activities of the mutants against five reactive oxygen and nitrogen species were evaluated by a chemiluminescence assay, electron paramagnetic resonance spectroscopy, or a HPLC-flow reactor assay. Our results showed that the contributions of Cys34 and the Met residues to the antioxidant activity of HSA were 61% and 29% against O(2)(•-), 68% and 61% against H(2)O(2), 38% and 6% against HO(•), 36% and 13% against HOCl, and 51% and 1% against (•)NO, respectively. Thus, the findings propose in a direct way that Cys34 plays a more important role than the Met residues in the antioxidant activity of HSA.

RNA-hydrolyzing activity of human serum albumin and its recombinant analogue

The comparative analysis of RNA-hydrolyzing activity of albumin from human serum and albumin expressed in methylotrophic yeast Pichia pastoris has been carried out . The rate of polyribonucleotide phosphodiester bond cleavage in the presence of recombinant albumin has been found to be similar to that of the reaction mediated by the native protein. According to 31P NMR data, RNA hydrolysis follows the mechanism of intermolecular trans-esterification to yield 2′,3′-cyclophosphodiester reaction products that are further slowly hydrolyzed to form nucleoside-3′- and nucleoside-2′-phosphates. Analysis of pH dependence suggests an acid–base mechanism of catalysis. The catalytic activity and substrate specificity of albumin in RNA hydrolysis distinguish it from human ribonucleases.

Redox Homeostasis of Albumin in Relation to Alpha‐Lipoic Acid and Dihydrolipoic Acid

Albumin represents the predominant circulating antioxidant agent in plasma exposed to continuous oxidative stress and a change in serum albumin structure accounts for its antioxidant properties. Alterations in the redox status of albumin may result in impairments of its biological properties. Alpha-lipoic acid (LA), a naturally occurring thiol compound found in virtually all species, is a potent antioxidant with high efficacy which is also involved in the chelation of metal ions, regeneration of antioxidants, and repair of oxidatively damaged proteins. In human body LA is rapidly reduced to dihydrolipoic acid (DHLA) after intake into the cell. Both, LA and DHLA are amphipathic molecules which act as antioxidants both in hydrophilic and lipophilic environments. The present study aimed to investigate the antioxidant/pro-oxidant effects of LA and DHLA due to their concentrations in metal-catalyzed protein oxidation (MCO) of human serum albumin (HSA). Progressive oxidative modification of albumin was found in MCO system by an increased content of protein hydroperoxides (POOH), protein carbonyl groups (PCO) which is the former's major breakdown product, and other protein oxidation markers such as advanced oxidized protein products (AOPP) and protein thiol groups (P-SH). The possible antioxidant protective effects of LA and DHLA were observed with 25 microM and 50 microM; DHLA being more influential. Protein oxidation parameters were found to be lower and P-SH levels seemed higher. However, prooxidant effects of both LA and DHLA came on the scene with increased concentrations of 75 microM and 100 microM where the latter seemed the most hazardous with contradicted results. It is clear that the loss of biological activity of human serum albumin by MCO system appears of medical relevance and if LA exerts similar effects seen in the present study, it is possible that cellular prooxidant activity can also result consuming this unique antioxidant in certain doses.

Redox homeostasis of albumin in relation to alpha-lipoic acid and dihydrolipoic acid

Albumin represents the predominant circulating antioxidant agent in plasma exposed to continuous oxidative stress and a change in serum albumin structure accounts for its antioxidant properties. Alterations in the redox status of albumin may result in impairments of its biological properties. Alpha-lipoic acid (LA), a naturally occurring thiol compound found in virtually all species, is a potent antioxidant with high efficacy which is also involved in the chelation of metal ions, regeneration of antioxidants, and repair of oxidatively damaged proteins. In human body LA is rapidly reduced to dihydrolipoic acid (DHLA) after intake into the cell. Both, LA and DHLA are amphipathic molecules which act as antioxidants both in hydrophilic and lipophilic environments. The present study aimed to investigate the antioxidant/pro-oxidant effects of LA and DHLA due to their concentrations in metal-catalyzed protein oxidation (MCO) of human serum albumin (HSA). Progressive oxidative modification of albumin was found in MCO system by an increased content of protein hydroperoxides (POOH), protein carbonyl groups (PCO) which is the former's major breakdown product, and other protein oxidation markers such as advanced oxidized protein products (AOPP) and protein thiol groups (P-SH). The possible antioxidant protective effects of LA and DHLA were observed with 25 µM and 50 µM; DHLA being more influential. Protein oxidation parameters were found to be lower and P-SH levels seemed higher. However, prooxidant effects of both LA and DHLA came on the scene with increased concentrations of 75 µM and 100 µM where the latter seemed the most hazardous with contradicted results. It is clear that the loss of biological activity of human serum albumin by MCO system appears of medical relevance and if LA exerts similar effects seen in the present study, it is possible that cellular prooxidant activity can also result consuming this unique antioxidant in certain doses.