Extracellular Albumin Research Articles

Kinetic analysis of myocardial fatty acid oxidation suggesting an albumin receptor mediated uptake process

The relationship between extracellular albumin and non-esterified fatty acid (NEFA) concentrations and the rate of fatty acid oxidation was studied. The data were obtained from tests performed on a working rat heart. When NEFA concentration was increased the rate of fatty acid oxidation showed a saturation curve at a constant NEFA/albumin ratio. Keeping constant the albumin concentration, a rise in NEFA concentration resulted in a linear increase of fatty acid oxidation. No correlation, however, was found between fatty acid oxidation and the unbound fraction of fatty acids. These results suggest an albumin receptor mediated NEFA uptake. With this assumption the following rate law of the NEFA uptake was derived: UPT = UPT0 X [FA]/(Km + [ALB] ) where [FA] and [ALB] are the total NEFA- and albumin concentrations, UPT0 and Km are constants. The rates of oxidation computed with this equation show a very good congruence to the values obtained experimentally. The validity of the rate law is confirmed by the fact that it is shown to be in agreement to the results of other investigators.

Enhanced albumin production by malignantly transformed hepatocytes during in vitro exposure to dimethylsulfoxide

The murine BW 1 and rat 32 III 6 d tumor cell lines, derived from a spontaneous mouse hepatoma and a carcinogen-induced rat hepatocellular carcinoma, were used to investigate the effect of dimethylsulfoxide (DMSO) on liver cells in vitro. After a 4-day exposure to DMSO in final concentrations of 0.5 and 1.0%, BW 1 cell-associated albumin increased by 41.6 and 94.2%; extra-cellular albumin levels in these same cultures rose by 131.4 and 214.2%. Exposure of 32 III 6 d cells to 2% DMSO produced increases in cell-associated and extra-cellular albumin concentrations of 67.8 and 188.7%, respectively. The lack of inducible γ-glutamyl transpeptidase in BW 1 cells and its decrease in 32 III 6 d cultures following DMSO treatment suggests that the DMSO-mediated enhancement of albumin production is not reflective of a random increase in the expression of cellular genes.

Role of the interstitial matrix during intestinal volume absorption.

The effects of net volume absorption rate (Jv,m) on intestinal interstitial fluid volume (VI), lymph flow (JL), and the excluded volume fraction for interstitial albumin (FE) were analyzed in an autoperfused cat ileum preparation. Tissue blood volume, extracellular space, and extracellular albumin (VA) were estimated using 51Cr-labeled red blood cells, 99mTc-labeled diethylenetriamine pentaacetic acid (DTPA), and 125I-labeled human serum albumin, respectively. Nonabsorptive values of 27.8 ml/100 g, 18.2 ml/100 g, and 0.37 were acquired for VI, VA, and FE, respectively. Net volume absorption results in an increase in intestinal interstitial volume and lymph flow and decreases the degree of albumin exclusion in the interstitial matrix. The magnitude of the changes in interstitial volume, lymph flow, and excluded volume of albumin during net volume absorption are related to the rate of absorption. The increased matrix hydration during absorption serves to enchance vascular and lymphatic removal of absorbed volume.

Differences in albumin distribution and dynamics between toxaemic and non-toxaemic pregnant women.

By using least squares curve fitting techniques, double exponential curves were fitted to points representing the decay of plasma 131I-albumin after blood volume estimation of 48 pregnant women. Data from the fitted curves provided estimates of the distribution of albumin between plasma and extravascular compartments, exchange between the two and rate of albumin catabolism. The lower total extracellular albumin mass of a group of 23 severely toxaemic patients was shown to arise solely from the difference in plasma albumin mass between this group and the remaining 25 patients. Comparison of these results with those in the literature suggests that pregnant women have a higher proportion of their exchangeable albumin mass in the plasma compartment and a higher rate of albumin catabolism than non-pregnant women.

Biosynthesis of rat serum albumin.

1. The labelling of intracellular and extracellular serum albumin was studied in liver slices and in whole rats by using new methods for the purification of the protein. 2. The results suggest that a polypeptide precursor is formed that is converted relatively slowly into serum albumin. 3. The effect of liver cell K(+) has been examined by a double-label method and it is shown that K(+) accelerates the rate of conversion of ;precursor' into albumin. The rate of transit of albumin across the cell membrane appears to be unrelated to the concentration of K(+) within the cell. 4. The time-course of incorporation of radioactive amino acid into albumin follows a sigmoidal mode. There is a pronounced time-lag before label starts to appear in intracellular albumin, and a further time-lag before it appears in extracellular albumin. 5. In slices the sum of intra- and extra-cellular label rises steadily from 30min after the start of labelling with a pulse of labelled leucine or valine and continues to rise for at least another 60min. This occurs whether labelling is stopped by addition of excess of carrier amino acid or with cycloheximide (100mum) or both. 6. The intracellular albumin content remains constant whether slices are maintained with low or normal intracellular K(+) concentrations. 7. Specific radioactivities of intracellular albumin (and fractions thereof) and of extracellular albumin were determined in vitro and in vivo. The results show that the intracellular albumin cannot be a precursor of extracellular albumin, unless a very small compartment is turning over much more rapidly than the bulk of the liver albumin or even of the microsomal albumin.

The separation of intracellular serum albumin from rat liver.

1. Antibody precipitation of serum albumin from rat liver extracts yields impure preparations of the protein. 2. When rat liver is labelled with l-[1-(14)C]leucine, antibody precipitation of albumin leads to material that is contaminated with a protein or proteins of very high specific radioactivity. Only 10-25% of the radioactivity of the antibody precipitate is associated with serum albumin. 3. A chromatographic procedure is described that can be used to separate radiochemically pure serum albumin from antibody precipitates obtained from extracts of rat liver. 4. Extracellular albumin secreted by liver slices yields a precipitate with antibody which contains much less radioactive impurity. About 70-90% of the radioactivity is associated with serum albumin. Serum albumin separated by antibody precipitation from rat serum labelled in vivo was not contaminated with the radiochemical impurities associated with intracellular albumin. 5. A simple method is described of obtaining the content of serum albumin in rat liver extracts by the technique of isotope dilution and ion-exchange chromatography.

Free fatty acid and ATP levels in adipocytes during lipolysis

Lipolytic hormones such as catecholamines and ACTH as well as lipolytic agents—e.g., 3′–5′ dibutyryl-cyclic AMP and methyl xanthines—are known to reduce ATP levels in adipose cells incubated in vitro. Considerable indirect evidence exists implicating intracellular FFA accumulation as a causative factor. To obtain more direct evidence for a causal relationship a simple and accurate method was developed for measuring intracellular FFA levels in isolated adipocytes using sucrose-U- 14C as an extracellular marker. Following incubation, medium and cells were separated by centrifugation and the infranatant medium was removed by aspiration. The volume of medium trapped between cells was determined by measuring the amount of sucrose- 14C retained in the packed adipose cell float. In this way the FFA content of the adipose cell float could be corrected for contamination by FFA bound to extracellular albumin. The basal FFA content of isolated adipocytes obtained from normal fed rats was 0.6 μEq./Gm. cell lipid. Addition of norepinephrine resulted in a rapid increase in intracellular FFA which plateaued at-22.5 μEq./Gm. cell lipid within 15 mins. Under optimal conditions of linear release of fatty acids—i.e., when medium albumin is not saturated by FFA—adipocyte ATP levels were not significantly depressed. Reduction of adipocyte ATP levels by lipolytic hormones correlated inversely with intracellular accumulation of FFA. Under these circumstances medium albumin approached saturation and intracellular FFA levels reached 6–9 μEq./Gm. cell lipid. Glucose, which is known to have a protective effect against ATP reduction, also prevented intracellular accumulation of FFA to cytotoxic levels. These results strongly support the view that the fall in adipocyte ATP after treatment with lipolytic hormone is the result of intracellular FFA accumulation, which depresses ATP synthesis by uncoupling oxidative phosphorylation. It is suggested that experiments undertaken to examine the relationship between effects of lipolytic hormones and other energy requiring processes must employ optimal in-vitro conditions—e.g., linear FFA release and nonsaturation of medium albumin—so as to prevent artifactual phenomena arising secondary to excessive intracellular FFA accumulation or ATP deficiency.

Intracellular accumulation of free fatty acids in isolated white adipose cells

A simple, rapid, and accurate method was developed for measuring intracellular FFA levels in isolated white adipose cells using sucrose-(14)C or inulin carboxyl-(14)C as nontransportable, nonutilizable markers of the extracellular space. Following incubation, medium and cells were separated by centrifugation and the infranatant medium was removed by aspiration. The volume of medium trapped between cells was determined by measuring the amount of sucrose-(14)C or inulin carboxyl-(14)C retained in the floating packed adipose cells. In this way the FFA content of the adipose cells could be corrected for contamination by FFA bound to extracellular albumin. With this technique the initial events in hormone-activated lipolysis were studied under conditions of maximal and constant rates of triglyceride hydrolysis. The FFA content of isolated adipocytes of fed rats was 0.5 micro mole/g cell lipid. On addition of norepinephrine in the presence of medium albumin, the concentration of intracellular FFA rapidly increased and reached a plateau at a concentration of 2-2.5 micro moles/g cell lipid. In the presence of medium albumin an initial lag in glycerol release occurred and this was attributed to partial hydrolysis of triglyceride with retention of lower glycerides. After 5 min of incubation FFA and glycerol output was constant. In the absence of medium albumin norepinephrine-stimulated lipolysis was reduced more than 90% and extracellular FFA release was not detected. Nevertheless, intracellular FFA accumulation was identical to that seen in the presence of albumin. The data suggest that most of this intracellular pool of FFA is bound to cytoplasmic constituents.