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PubMedDate not supplied

Lactosylation of albumin reduces uptake rate of dibromosulfophthalein in perfused rat liver and dissociation rate from albumin in vitro.

Two types of models have recently been proposed to describe hepatic uptake kinetics of protein bound drugs: a model in which dissociation from plasma protein is rate limiting the process, and a model in which an interaction between protein and hepatocyte surface is thought to promote dissociation and uptake of the drug. This study was designed to investigate several aspects of both models, using lactosylated albumin as a binding protein that can interact with the Ashwell receptor abundantly present on the hepatocyte. Dibromosulfophthalein clearance was studied in rat liver in the presence of 150 microM (1%) albumin or 150 microM lactosylated albumin. Initial disappearance rate from perfusate in the presence of lactosylated albumin indicated a 2-fold decrease in hepatic uptake rate compared with native albumin. This was confirmed by compartmental analysis, showing a similar decrease in hepatic uptake rate constant. Protein binding of dibromosulfophthalein to lactosylated albumin was only marginally different from normal albumin. Consequently, modification of the protein retarded uptake of the organic anion at an essentially unchanged unbound concentration. Fluorescence spectroscopy of lactosylated albumin showed a blue-shifted tryptophan emission spectrum compared with albumin, indicating increased hydrophobicity of the neoglycoprotein. We therefore considered a change in off-and-on rate for binding of dibromosulfophthalein in lactosylated albumin. Rapid filtration experiments indicated that the dissociation rate constant of dibromosulfophthalein from lactosylated albumin was half that of controls. We conclude that the decreased off-rate from lactosylated albumin can explain the retarding influence on hepatic uptake rate of dibromosulfophthalein. This observation argues for the concept of dissociation-limited uptake in the hepatic clearance of the organic anion.

Animals↗
PubMed1985

The distribution of native albumin and foreign albumin injected into lateral ventricles of prenatal and neonatal rat forebrains.

Several plasma proteins are found within the cells of the developing brain of many species, with a distribution pattern which changes during development, but the origin of such proteins is in dispute. The experiments described here were designed to test the hypothesis that some developing brain cells are able to take up plasma proteins. The distribution of the plasma protein albumin has been studied in the rat forebrain from the 14th day of gestation until birth. Although present within the cerebrospinal fluid and plasma from the earliest age studied, albumin was not seen within cells of the developing forebrain until day 16E or 17E. A foreign protein, sheep albumin, was injected into the ventricles at days 14E, 16E, 18E, 20E and on the day of birth. Sheep albumin can be detected in the presence of rat albumin because the antibody to sheep albumin does not cross-react with rat albumin. The sheep albumin was taken up very rapidly into cells of the ventricular zone at the later but not the earlier ages, thus mimicking the distribution of the naturally occurring rat albumin. After the foreign albumin had been left within the ventricle for several hours, some of the cells of the cortical plate also contained the protein, again mimicking the normal distribution of albumin. These findings suggest that the presence of albumin within cells of the developing rat forebrain can largely be attributed to uptake rather than synthesis.

Animals↗
PubMed1981

Albumin-lipid interactions: prostaglandin stability as a probe for characterizing binding sites on vertebrate albumins.

We determined the effect of vertebrate albumins on the stability of several physiologically relevant prostaglandins. All naturally occurring prostaglandins with beta-hydroxy ketone group decomposed by first-order kinetics, dependent on the albumin concentration in 0.1 M, pH 7.4, buffer at 37 degrees C. Even subphysiological levels of albumin (1-20 mg/mL) significantly reduced the stability of these compounds in vitro. The prostaglandins with a beta-hydroxy ketone responded to albumin in the order of their intrinsic stability; namely, less stable compounds were more susceptible. The destructive effect of albumin was nearly maximal at a 1:1 mole ratio of albumin (20 mg/mL):prostaglandin (100 micrograms/mL). Albumin had no destructive effect on prostaglandins without a beta-hydroxy ketone. Albumins from different vertebrates varied in destructive severity, but all were effective. Near neutrality, in the absence of albumin, decomposition of E-type prostaglandins was practically suspended at the dehydration stage. In the presence of albumin, dehydration was accompanied by rapid isomerization reactions (e.g., PGA1 leads to PGB1) that occur only at an elevated pH. The results suggest that albumin sequesters prostaglandins to one principal binding site and exposes them to its associated highly alkaline microenvironment. This results in a uniform and predictable influence on prostaglandin stability. Our proposed model system successfully reconciles apparently anomalous or contradictory reports regarding the effect of albumin on prostaglandin stability.

Animals↗
PubMed2000

Synthesis rate of plasma albumin is a good indicator of liver albumin synthesis in sepsis.

Plasma albumin is well known to decrease in response to inflammation. The rate of albumin synthesis from both liver and plasma was measured in vivo by use of a large dose of L-[(2)H(3)-(14)C]valine in rats injected intravenously with live Escherichia coli and in pair-fed control rats during the acute-phase period (2 days postinfection). The plasma albumin concentration was reduced by 50% in infected rats compared with pair-fed animals. Infection induced a fall in both liver albumin mRNA levels and albumin synthesis relative to total liver protein synthesis. However, absolute liver albumin synthesis rate (ASR) was not affected by infection. In plasma, albumin fractional synthesis rate was increased by 50% in infected animals compared with pair-fed animals. The albumin ASR estimated in the plasma was similar in the two groups. These results suggest that hypoalbuminemia is not due to reduced albumin synthesis during sepsis. Moreover, liver and plasma albumin ASR were similar. Therefore, albumin synthesis measured in the plasma is a good indicator of liver albumin synthesis.

Acute-Phase Proteins↗
PubMed1987

Effects of albumin concentration on endothelial albumin transport in vitro.

Albumin transfer across cultured porcine pulmonary artery endothelial cell monolayers was studied at different concentrations of luminal and interstitial albumin. Increased interstitial and luminal albumin concentrations increased the rates of transfer of albumin from interstitium to lumen and lumen to interstitium, respectively. Interstitial-to-luminal albumin clearance reached a maximum rate at 725 microM interstitial albumin. The clearance of dextran from interstitium to lumen also increased when interstitial-to-luminal albumin clearance increased, suggesting that albumin was not transferred alone across the endothelium. The increase in interstitial-to-luminal albumin clearance did not occur in the absence of endothelial cells, at 4 degrees C, or when dextran or dextran sulfate sodium were added to the interstitial compartment. These data demonstrate that albumin concentrations can influence the rates of endothelial albumin transfer and that albumin can be transported across the endothelium by a process mediated by endothelial cells.

Animals↗
PubMed2006

Coelution of other proteins with albumin during size-exclusion HPLC: Implications for analysis of urinary albumin.

BACKGROUND: Size-exclusion HPLC has been used as an alternative to immunoassays for quantifying urinary albumin (microalbumin). Systematically higher values for the HPLC method have been proposed to result from nonimmunoreactive albumin. METHODS: We evaluated separation of purified proteins and urinary components by size-exclusion HPLC using a Zorbax Bio Series GF-250 column eluted with phosphate-buffered saline. Urinary components eluting in the "albumin" peak were analyzed by mass spectrometry and reversed-phase HPLC. RESULTS: Several proteins, such as transferrin, alpha1-proteinase inhibitor, alpha1-acid glycoprotein, and alpha2-HS glycoprotein, analyzed as purified components, were not resolved from albumin by size-exclusion HPLC. Peaks for other proteins, such as IgG and urinary components identified as dimers of alpha1-microglobulin and immunoglobulin light chains, overlapped with the albumin peak. Profiles of urine specimens showed variable amounts of components overlapping with albumin. Furthermore, the albumin peak obtained by size-exclusion HPLC was found by mass spectrometry and reversed-phase HPLC to contain multiple components in addition to albumin. CONCLUSIONS: Size-exclusion HPLC does not resolve albumin from several other proteins in urine. The albumin peak resolved by this technique, although predominantly composed of albumin, contains several coeluting globulins that would contribute to overestimation of albumin concentration by size-exclusion HPLC.

Albuminuria↗
PubMed1968

Precursor-product relationship between intrahepatic albumin and plasma albumin.

Rats were injected with [(3)H]leucine, and at various times thereafter labelled albumin was isolated by electrophoresis from their livers and blood plasma. The specific radioactivity of each protein was determined by spectrophotometry and liquid-scintillation spectrometry. Intrahepatic albumin was shown to be identical with plasma albumin by its electrophoretic mobility and antigenicity. It was found that intrahepatic albumin was the direct precursor of plasma albumin. Comparison of their specific radioactivities showed that intrahepatic albumin attained a higher specific radioactivity before plasma albumin. When plasma albumin reached its maximum specific radioactivity, that of intrahepatic albumin had decreased to a similar value. Thereafter, the specific radioactivity of intrahepatic albumin remained lower than that of plasma albumin.

Acetates↗
PubMed2004

Changes in serum albumin concentration and volume expanding effects following a bolus of albumin 20% in septic patients.

BACKGROUND: Patients with systemic sepsis develop a capillary leak syndrome, and serum -albumin concentration decreases. Hyperoncotic albumin infusion can be used for volume expansion in these patients, but the degree and duration of effect are not well described. We assessed volume expansion by albumin 20% infusion and compared the retention of infused albumin in septic patients and healthy controls. METHODS: We gave albumin 20%, 200 ml as a rapid infusion to 70 patients with septic shock and 26 controls. Blood samples were taken before and 1, 5, 15, 30, 60, 120 and 240 min after the infusion for measurement of serum albumin concentration and haematocrit. Haemodilution and the percentage of administered albumin remaining intravascularly at each time were calculated. RESULTS: The mean proportion of the increase in albumin remaining at 4 h was 68.5 (sd 10)% in septic patients and 79 (5)% in controls (P<0.001). The albumin 20%, 200 ml caused a secondary fluid resorption and volume expansion maximal at 30 min, equivalent to a 430 ml infusion in septic patients and 500 ml in controls. CONCLUSIONS: After giving albumin, serum albumin concentrations decrease significantly faster in septic patients than in healthy controls.

Adult↗
PubMed1976

Structural differences between albumin A and albumin C of the house mouse, Mus musculus.

Two albumins, albumin A from C3H mice and albumin C isolated from descendents of the wild mice in which the variant was first uncovered, were found to differ in their electrophoretic properties. Albumin C was shown to bind two more H+ ions than albumin A at pH 5.4. Peptide mapping after trypsin digestion revealed that albumin C had three peptides (TP-C1, TP-C2, and TP-C3) which were missing in albumin A. The latter likewise had a peptide (TP-A1) which was not found in albumin C. An amino acid analysis of the variant peptides suggests that TP-A1 had been split into TP-C1 and TP-C2 on digestion with trypsin, because a glutamic acid in TP-A1 was replaced by a lysine. This change would also appropriately alter the electrophoretic properties of albumin C. No obvious counterpart was discovered for TP-C3 of albumin C in albumin A.

Amino Acids↗
PubMed1995

Identification of a 130-kDa albumin in tuatara (Sphenodon) and detection of a novel albumin polymorphism.

Electrophoretic, immunochemical, and protein sequence analyses were performed on plasma albumin of the tuatara (Sphenodon), a rare reptile endemic to New Zealand. The analyses revealed that, unlike other terrestrial vertebrates, tuatara do not seem to possess a 60- to 75-kDa plasma albumin. The common form of plasma albumin in this genus has an apparent molecular mass of 130 kDa, making it by far the largest albumin reported for any terrestrial vertebrate. Starch gel electrophoresis of samples from tuatara on 24 of the 30 islands inhabited by this genus resolved two forms of the 130-kDa albumin (albumins A and C). A third albumin of approximately 170 kDa (albumin B), reflecting a novel alloalbuminemia, was found in tuatara in three geographically isolated populations. Albumin A appears to be restricted to populations at the southern extremity of the tuatara's distribution, while albumin C was found in all but four (southern) populations. Possible explanations for the origin and distribution of these albumins are discussed.

Alleles↗
PubMed1976

Structural requirements for steroid binding and quenching of albumin fluorescence in bovine plasma albumin.

1. Steroids interact with bovine plasma albumin at a binding region that involves tryptophanyl, tyrosyl, arginyl and lysyl residues. The function of the tryptophanyl residues is demonstrated by: (a) the decrease of albumin binding affinity after modification of one tryptophanyl with 2-nitrophenylsulfenyl chloride; (b) steroid quenching of albumin tryptophanyl fluorescence; and (c) steroid quenching of 1-anilinonaphth-alene-8-sulfonate fluorescence, when it is excited by energy transfer from excited tryptophanyls. The function of tyrosyl residues is demonstrated by the decrease of albumin binding affinity after nitration of 30% tyrosyls with tetranitromethane, or deprotonation of tyrosyls by variation of pH. The function of arginyl and lysyl residues is demonstrated by the decrease of binding affinity after modification of these residues with glyoxal, formaldehyde or acetic anhydride. The presence of both apolar (Trp, Tyr and Lys (deprotonated)) and polar (Arg and Lys(protonated)) residues at the steroid binding site fits in well with the site relative apolarity, when expressed on the Kosower scale (Kosower, E.M. (1958) J. Am. Chem. Soc. 80, 3253-3260). 2. The contribution of specific amino acid residues to steroid binding depends to some extent on the steroid structure, as exemplified by the quantitatively different role of arginyl (or lysyl) residues in albumin interaction with testosterone acetate and epitestosterone, respectively, or that of tyrosyl residues in albumin interaction with 11-deoxycorticosterone and epitestosterone, respectively. 3. The concerted action of polar and apolar amino acid residues is an essential requirement for steroid binding, since unfolding of albumin polypeptide chain by guanidine-HC1, urea, or by reduction of disulfide bridges with 2-mercaptoethanol, strongly decreases steroid binding to albumin while, conversely, reoxidation and refolding of the unfolded polypeptide chain restore albumin affinity for steroids. 4. Parallel determinations of steroid binding constants by equilibrium dialysis and fluorimetric titration, as well as the general pattern of the pH and temperature effects on steroid quenching of albumin fluorescence, confirm the validity of the fluorescence quenching titration as an effective method for measuring albumin-steroid molecular interactions.

Androgens↗
PubMed2000

Albumin inhibits apolipoprotein AI and AII production in human hepatoblastoma cell line (Hep G2): additive effects of oleate-albumin complex.

Although the role of multiple humoral agents (such as plasma albumin, glucose, hormones etc.) are implicated in lipoprotein metabolism, the mechanism of action of these agents on various steps of the synthesis and secretion of lipoproteins and apolipoproteins (protein moieties of lipoproteins) are not completely understood. Specifically, the hepatocellular mechanisms of the effect of albumin and fatty acids on apolipoprotein (apo) AI and AII [major proteins of high density lipoproteins (HDL)] synthesis and secretion are not known. Using human hepatoblastoma cells (Hep G2) as an in vitro model system, this study examined the effect of albumin and fatty acids on the synthesis, secretion, and the steady-state mRNA expression of apo AI and AII. The data indicated that the incubation of Hep G2 cells with albumin, dose-dependently, inhibited apo AI and AII accumulation (secretion) in the media, de novo synthesis, and the steady-state mRNA expression. Albumin did not alter total protein synthesis; thus the effect of albumin appeared to be specific for the synthesis and secretion of apo AI and apo AII. Free fatty acids (FFA) are transported by albumin and diseases characterized by enhanced FFA mobilization (e.g. diabetes mellitus) are associated with low HDL levels. Studies were therefore performed to examine the effect of albumin-bound-oleic acid on apo AI and apo AII production. The results showed that the albumin-oleate complex further increased the inhibitory effects of albumin on apo AI and apo AII production. These data suggest how HDL metabolism may be affected at the hepatocellular level by alterations in plasma albumin concentrations and/or fatty acid mobilization in clinical situations characterized by altered HDL levels.

Albumins↗