Quantitative aspects of the interaction of bile acids with human serum albumin (original) (raw)
Related papers
Structural features of the hydroxy- and keto-disubstituted bile salts: human serum albumin binding
Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1995
The binding of keto-and hydroxy bile salts to human serum albumin, the identity of the bile salts binding sites and the identification of the amino acids present in these sites were studied. The keto bile salts cholanate-3-one (C3), cholanate-3,6-dione (C3-6) and cholanate-3-hydroxy-6-one (KHC) were found to quench the native fluorescence emission of albumin. This suggested that the tryptophan residue of human albumin (residue 214) is accessible to the keto bile salts and not to the hydroxy parent compounds. The binding of the keto bile salts was characterized by a simple population of binding sites with K a ranging from 22 • 104 M-~ for the mono keto bile salt (C3) down to 4. 104 M-~ for the hydroxy-keto bile salt (KHC). The substitution of an oxo group at carbon C 3 in C3-6 molecule for a hydroxy group (KHC) produce a significant decreasing of the interaction, suggesting that the hybridization state of the carbon at C 3 in the steroid ring of the bile salt molecule is also an essential requirement for bile salts binding. It was found that bile salts are bound to the benzodiazepine binding site on human albumin (site II), producing a perturbation on site I, fatty acids and bilirubin binding site. The presence of only one substituent at C 3 (oxo or OH) produce an important perturbation on the fatty acid binding sites, decreasing the polarity of the its microenvironment, while a little effect was observed for the dihydroxy and di-oxo-substituted BS, suggesting that the hydroxy substituents at C 6, C 7 and C12 do not interact in a significant manner with the fatty acid binding sites on HSA. The participation of specific amino acids in albumin-bile salt binding sites depends on the polar groups on the bile salt molecules as exemplified by the quantitatively different role of lysyl residues like those interacting with KHC, C3 and C3-6, and tyrosyl residue interacting with KHC. The following amino acids in human albumin were found to play a role in the bile salts-albumin interaction: lysyl 195 and 225, several arginyls, histidyl 146 and tyrosyl 411.
Comparative binding of bile acids to serum lipoproteins and albumin
2000
Characteristics of the binding of lithocholic acid (LC), chenodeoxycholic acid (CDC), and cholic acid to human plasma proteins were studied. Affinity of the different plasma protein fractions for the bile acids studied decreased with increased polarity of the steroid nucleus of the bile acid. Binding of LC, CDC, and cholic acid to the lipoprotein-free, albuminrich plasma fraction was characterized by two classes of binding sites with respective K D s of 2, 5, and 51 pM, and of 39, 2,387, and 5,575 p M , while corresponding B,, values were similar for the different bile acids, at around 6 and 100 nmol/mg protein. Bile acid binding to the different lipoprotein fractions was characterized by a single population of binding sites, with a K O ranging from 47 to 66 pM for LC, 695 to 1010 pM for CDC, and 2,511 to 2,562 pM for cholic acid. B,, values, at 416-913 nmol/ mg protein, were similar among the different bile acids studied. Both glycine-and taurine-conjugated, as well as unconjugated LC competitively inhibited [24-"C]LC binding to low density (LDL) and to high density lipoproteins (HDL) to the same extent, while the more polar LC-3-sulfate, CDC, and cholic acid were increasingly less potent in displacing LC binding from the respective lipoproteins. Furthermore, all bile acids studied shared the same lipoprotein binding site. The lipoprotein fluorescence at 330-334 nm, following excitation at 280 nm, was diminished after incubation with LC, suggesting that the bile acid masks the tryptophan residues of the protein moiety. Finally, the initial rate of uptake of 1 pM LC, in isolated hamster hepatocytes, at around 0.045 nmol . sec-lmg cell wt-', was not affected by the protein carrier. However, for the same concentration of LC, bound to either LDL 0.r HDL, LC binding resulted in 75-77% of the total [24-'4C]LC nonspecifically bound to the hepatocyte, compared to 65% when bound to albumin, and 45% in the absence of protein. U The studies show
Hepatic bile acid uptake: effect of conjugation, hydroxyl and keto groups, and albumin binding
Journal of lipid research, 1982
Hepatic extraction of trihydroxy (free, glyco- and tauro-conjugated) dihydroxy, and monohydroxy bile acids has been evaluated in single pass liver perfusion experiments in rats. The percentage of each bile acid bound to albumin was also evaluated by equilibrium dialysis. Conjugation increased bile acid liver extraction, without relevant differences in the percentage of bile acid bound to albumin. Among the free bile acids, trihydroxy bile acids were more efficiently cleared by the liver than the dihydroxy acids, and the latter more than monohydroxy bile acids. 7-Ketolithocholic acid uptake was slightly less than that of cholic acid. Conversely, among dihydroxy bile acids, the percentage of the bile acid bound to albumin decreased from lithocholic acid to cholic acid. Decreasing the albumin concentration in the medium, and hence the fraction of the bile acid bound to albumin, resulted in an increase in bile acid liver extraction. Therefore besides differences in the chemical structur...
Radioimmunoassay of bile acids in serum
Clinical Chemistry
We developed four radioimmunoassay procedures for the determination of glycine-conjugated bile acids in serum. Antibodies to two primary bile acids, cholylgycine and chenodeoxycholylglycine, and to two secondary bile acids, sulfolithocholylglycine and deoxycholylglycine, were raised in rabbits after the acids were covalently linked to albumin by use of the carbodiimide reaction. Assay sensitivity for each of these bile acids is in the picomole range with the standard curve extending from 10-80 pmol. The concentration of bile acids in serum increased in various states of liver disease and its measurement appears to be an extremely sensitive indicator of liver function.
The quantitative estimation of bile acids and their conjugates in human biological fluids
Journal of lipid research, 1983
This review attempts to provide a concise and critical summary of modern methods for the analysis of bile acids and their conjugates in human biological fluids. Most emphasis is given to more up-to-date procedures that have been applied to the study of human disease and attention is drawn to previous reviews in areas that have not been covered here. An increasing awareness of the possibility that bile acids may be involved in the etiology of a number of disorders, or that such disorders may give rise to changes in bile acid concentration, has stimulated the study of bile acid methodology. Although many procedures have been described using, for example, high-pressure liquid chromatography (HPLC), gas-liquid chromatography (GLC), gas-liquid chromatography--mass spectrometry (GLC-MS), and radioimmunoassay (RIA), no simple but comprehensive procedure for the estimation of bile acids and their conjugates has yet been published. Further study in this area is still required in order to est...
Journal of Lipid Research, 1984
The structure of the bile acid molecule is described and correlated with physicochemical properties of bile acids such as solubility, ionization, and micelle formation. Recent measurements of the critical micellar concentration (CMC) of a large number of bile acids indicate that the CMC is influenced by both side chain and nuclear structure. Bile acids with hydroxy substituents on both sides of the steroid nucleus are non-amphipathic and do not form micelles, and decreasing the length of the side chain causes an exponential increase in the CMC. Bile acid ionization, measured by titration in alcoholwater mixtures, is shown to be uninfluenced by nuclear substituents; the pK, of all unconjugated bile acids is about 5. lnteractions of bile acid solutions with Ca4+ are discussed; A bit of history Supplemcntuy key words critical micellar concentration cholanoids Twenty-five years ago, the field of bile acids ("cholanology") was in its youth, although studies on bile and bile acids had been a continuing area of activity in chemical (1, 2), biochemical (3, 4), physiological (5), on the relationship between the physicochemica~ prop-Abbreviations: CMC, critical micellar concentration; CMT, critical micellar temperature; CMpH, critical micellar pH; OWDR, octanolerties and the properties Of acids* That water distribution ratio; HPLC, high performance liquid chromatogsuch a relationship does exist has become a working raphy.
Biochimica et Biophysica Acta (BBA) - Protein Structure and Molecular Enzymology, 1999
The binding of 3,6-hydroxy and keto disubstituted bile salts to human serum albumin was studied using differential scanning calorimetry, fluorescence spectroscopy and circular dichroism. The bile salts assayed did not produce any modification in the shape of the albumin thermogram, its thermal unfolding process in their presence being reversible ; however, an increase in the enthalpy of unfolding and in the T m was observed in the presence of 3,6-diketo and 3-hydroxy-6keto bile salts. These two derivatives induced a negative circular dichroism spectrum of the protein around 280^290 nm, quenched the native fluorescence of the buried tryptophan of albumin and induced energy transfer between 1 aniline-8naphthalene sulfonate and the buried tryptophan 214 of albumin. The presence of a keto group at C 6 in the steroid ring of the bile salts plays an important role in producing slight movement of the albumin domains, increasing the distance between domains I and II.
Bile Acids: Physiological Activity and Perspectives of Using in Clinical and Laboratory Diagnostics
Molecules
Bile acids play a significant role in the digestion of nutrients. In addition, bile acids perform a signaling function through their blood-circulating fraction. They regulate the activity of nuclear and membrane receptors, located in many tissues. The gut microbiota is an important factor influencing the effects of bile acids via enzymatic modification. Depending on the rate of healthy and pathogenic microbiota, a number of bile acids may support lipid and glucose homeostasis as well as shift to more toxic compounds participating in many pathological conditions. Thus, bile acids can be possible biomarkers of human pathology. However, the chemical structure of bile acids is similar and their analysis requires sensitive and specific methods of analysis. In this review, we provide information on the chemical structure and the biosynthesis of bile acids, their regulation, and their physiological role. In addition, the review describes the involvement of bile acids in various diseases of...
Lipids, 1989
The binding of lithocholic acid to different plasma fractions was studied. When whole plasma was incubated for 8 hr, approximately 25% of the incubated [14C]lithocholic acid was bound to the lipoprotein and lipoprotein-free, albumin-rich fractions. An average of 87.6% of the bound-lithocholic acid was present in the lipoprotein-free, albumin-rich fraction, 7.2% in high density lipoproteins, 2.2% in low density lipoproteins, 1.0% in intermediate density lipoproteins and 2.0% in very low density lipoproteins. Expressed as binding per μg protein, considerably less [14C]lithocholic acid was bound to the lipoprotein-free, albumin-rich fraction, than to the lipoproteins. The binding of [14C]lithocholic acid after the incubation of the isolated plasma fractions was similar to that found after the incubation of whole plasma. The highest transfer of [14C]lithocholic acid occurred from the lipoprotein-free, albumin-rich fraction to the lipoprotein fractions. The studies indicate, that, although the largest amount of lithocholic acid is bound to the lipoprotein-free, albumin-rich fraction, per μg protein, the binding of lithocholic acid to lipoporteins is more pronounced and stable than that bound to the lipoprotein-free, albumin-rich fraction. Since lipoproteins, in contrast to albumin, are internalized by most tissues, they may be important carriers into cells of lithocholic acid and other potentially toxic or tumorigenic bile acids.