THE COMBINATION OF ORGANIC ANIONS WITH SERUM ALBUMIN

Partition coefficients of four perfluoroalkyl acid alternatives between bovine serum albumin (BSA) and water in comparison to ten classical perfluoroalkyl acids

Perfluoroalkyl acids (PFAAs) are persistent, ubiquitous environmental contaminants and their long-chain representatives are bioaccumulative. The phase-out of these compounds (e.g. PFOA and PFOS) shifted the production to alternatives. However, little is known about the bioaccumulative behaviour of the alternatives, which are still highly fluorinated. PFAAs are predominantly detected in blood, where they bind to the transport protein serum albumin. This sorption can be described by the albumin/water partition coefficient. It is unclear whether the partition coefficients of the alternatives are lower than or in the same range as those of classical PFAAs. We determined albumin/water partition coefficients for seven perfluoroalkyl carboxylates, three perfluoroalkane sulfonates and four alternatives by dialysis experiments in a physiologically representative system. Quantification was done by LC-MS/MS and a mass balance approach. Logarithmic albumin/water partition coefficients for PFAAs range from 2.8 to 4.8 [L_water kg_albumin^-1] and increase with increasing chain length. Perfluorinated sulfonates sorb more strongly than their carboxylate counterparts. The albumin/water partition coefficients for the alternatives (HFPO-DA, DONA, 9Cl-PF3ONS and PFECHS) are in the same range as for classical PFAAs. Structural modifications such as the introduction of ether groups into the chain do not reduce sorption to albumin, whereas the chlorine atom in 9Cl-PF3ONS seems to even increase the sorption to albumin. We further investigated whether the sorption strength could be affected in the presence of medium- or long-chain fatty acids. Binding competition between medium-chain fatty acids and PFAAs appeared to be possible. However, the presence of physiologically more relevant long-chain fatty acids should not alter the albumin/water partition coefficients of PFAAs.

Albumin as fatty acid transporter

SUMMARY

Fatty acids play critical roles in mammalian energy metabolism. Moreover, they are important substrates for the synthesis of membrane phospholipids and biologically active compounds like eicosanoids and leukotrienes. Because of their low solubility in aqueous solutions such as blood plasma and interstitial fluid, fatty acids are in need of binding proteins to increase their concentration in vascular and interstitial compartments. Albumin acts as main fatty acid binding protein in extracellular fluids. Plasma albumin possesses about 7 binding sites for fatty acids with moderate to high affinity, enhancing the concentration of fatty acids by a several orders of magnitude. Despite the high affinity of albumin for fatty acids, uptake of fatty acids by parenchymal cells such as skeletal and cardiac myocytes seems not to be hampered by albumin. In contrast, experimental findings suggest that albumin may facilitate the uptake of fatty acids by organs in need of these substrates. In the present overview the following issues will be briefly discussed: (i) transport and storage of fatty acids in the mammalian body, (ii) biosynthesis of albumin in the liver, (iii) localization and concentration of albumin in body fluids, (iv) interactions between albumin and fatty acids, (v) albumin structure and fatty acid binding sites, (vi) uptake of fatty acids by organs and roles for plasma albumin and (vii) lessons from patients and experimental animals lacking plasma albumin.

NUTRITION OF LEPTOSPIRA POMONA. II. FATTY ACID REQUIREMENTS

Johnson, R. C. (Fort Detrick, Frederick, Md.) and N. D. Gary. Nutrition of Leptospira pomona. II. Fatty acid requirements. J. Bacteriol. 85:976-982. 1963.-The albumin fraction of rabbit serum, obtained by (NH(4))(2)SO(4) fractionation, supported good growth of Leptospira pomona Wickard when added to a medium containing phosphate buffer, NH(4)Cl, and thiamine. Extraction of the albumin fraction with ethanol and ether (3:1) resulted in a loss of its growth-supporting activity, which could be restored upon the addition of the extract or various fatty acids. The growth-supporting activity of fatty acids containing 2 to 18 carbon atoms was investigated with the extracted albumin medium. The activity of the fatty acid was found to be related to the number of carbon atoms in the molecule. Maximal growth was obtained with palmitic, heptadecanoic, stearic, and oleic acids. The amount of growth of L. pomona increased at a fixed concentration of albumin as the molecular ratio of extracted albumin to the long-chain fatty acids increased from 1:1 to 1:6. At higher ratios, growth decreased sharply. Direct utilization of fatty acids during growth of L. pomona was shown by the incorporation of palmitic acid-1-C(14) or -2-C(14) into cellular material. A medium composed of 0.02 m Na(2)HPO(4)-KH(2)PO(4) buffer (pH 7.4), 0.8% extracted albumin, 4 x 10(-4)m palmitic acid, 10(-3)m NH(4)Cl, and 5 mug/ml of thiamine supported good growth. L. pomona was transferred ten times, and seven other serotypes were transferred five times, in this medium without any decrease in the amount of growth. Growth of L. pomona was initiated with approximately four organisms per ml.

CELLULAR TRANSPORT OF LONG CHAIN FATTY ACIDS

Cellular transport of long chain nonesterified fatty acids involves transfer of fatty acids between extracellular binding sites on albumin and tissue binding sites on cell membranes and organelles. Tissue phospholipids and lower glycerides do not serve as primary acceptors for fatty acid entering the cell. Evidence for an energy-dependent transport process is lacking; however, alterations in active cellular metabolism which influence utilization of fatty acids may indirectly affect transport by changing the rate of clearance of fatty acids from tissue binding sites. Release of nonesterified fatty acids from adipose tissue, and uptake by heart muscle and other tissues are influenced by fatty acid concentration and the molar ratio of fatty acid to albumin in extracellular fluid, and probably as well by the capacity and turnover rate of binding sites for fatty acid within the cells. The relationship between transport and molecular structure of fatty acids may be attributed to differences in solubility, protein binding, and rate of intracellular utilization of fatty acids of different chain length and degree of unsaturation. Removal of circulating triglyceride appears to be influenced by lipoprotein lipase activity of peripheral tissues but may be limited by the capacity of the tissue to accept the component fatty acids.

ESR studies of stearic acid binding to bovine serum albumin

The ESR spectra of a series of chain-labelled doxyl stearic acids (5-, 7-, 12- and 16-DSA) and doxyl methyl stearates (5-, 7-, 12- and 16-DMS) bound to the high-affinity binding sites of bovine serum albumin (BSA) have been analyzed using nonlinear least-squares fitting of slow-motional ESR stimulation. The motional analysis reveals that the rotational diffusion of these stearates around the axis perpendicular to the long hydrocarbon chain is greatly hindered, suggesting that they are held tightly in a channel of the protein. Comparison of the isotropic hyperfine splitting, A0, among each series shows that 5- and 16-DSA and 16-DMS have larger A0 values than the other spin labels. In addition, labels at the 16-C position of both DSA and DMS exhibit significantly increased motion relative to the other positions. These observations suggest that the channel starts at 5-C of the chain and ends somewhere between 13-C and 15-C, leading to an estimate of 11 +/- 1 A for the length of the channel. The methyl stearate labels exhibit significantly faster rotation around the chain axis than the analogous stearic acid labels, suggesting a double hydrogen-bonding mechanism for fatty acid binding to BSA. The ability of the acid to form two hydrogen bonds apparently fixes it more rigidly in the protein, preventing rotation about either single hydrogen bond. A double-hydrogen bonding mechanism is most consistent with the formation of a salt bridge between the negatively charged carboxylate of the acid and either a positively charged guanidino group of arginine, or the positively charged omega-amino groups of two lysine residues. An ESR study of the pH dependence of DSA binding indicates that salt bridge formation with lysine is responsible for at least some of the long chain fatty acid binding sites of BSA.

Pharmacokinetic basis for the comparative antitumour activity and toxicity of chlorambucil, phenylacetic acid mustard and beta, beta-difluorochlorambucil (CB 7103) in mice

This report describes the relationship between the pharmacokinetics, antitumour activity and toxicity of chlorambucil (CHL), phenylacetic acid mustard (PAAM) and beta, beta-difluorochlorambucil (beta-F2CHL) in mice. Pharmacokinetics were studied by HPLC, antitumour activity by a regrowth delay assay using the KHT murine sarcoma and toxicity by acute LD50. For both antitumour activity and acute toxicity the order of potency was: PAAM greater than CHL greater than beta-F2CHL. CHL and PAAM exhibited identical therapeutic indices, whereas that for beta-F2CHL was somewhat improved. CHL is metabolized by mitochondrial beta-oxidation to the 3,4-dehydro derivative (DeHCHL) and PAAM, and the latter is further metabolized to its monodechloroethylated derivative DeC-PAAM, presumably by hepatic microsomal enzymes. Administered PAAM gave only one metabolite, DeC-PAAM. Unexpectedly, despite beta, beta-disubstitution, beta-F2CHL was also beta-oxidized to give DeHCHL and PAAM, but at reduced rates. Further, metabolic switching was demonstrated with the appearance in large amount of 2 new, unidentified metabolites, which may be dechlorethylation products. The pharmacokinetics of administered CHL, PAAM and beta-F2CHL differ in that the plasma clearance was fastest for CHL, slowest for PAAM and intermediate for beta-F2CHL. For the metabolites, CHL produced peak plasma concentrations of DeHCHL and PAAM, respectively, 7-fold and 2-fold greater than those produced by beta-F2CHL. However, despite these differences, exposures to total bifunctional nitrogen mustards were similar following administration of the 3 drugs and therefore cannot account for their differential activity. In contrast, there was a good correlation between potency and PAAM exposure, which is highest after treatment with PAAM, intermediate after CHL and lowest after beta-F2CHL. In plasma, 3.2% of PAAM is present as nonprotein-bound free drug, compared to 1.3% for DeHCHL, 0.9% for CHL and 0.45% for beta-F2CHL. We propose the amount of free bifunctional nitrogen mustard, itself partly dependent on the extent of metabolism, to be of major importance for the in vivo potency of CHL analogues.

Protein interaction: concepts from thermodynamic measurements

Proteins are biological molecules par excellence. They have evolved as elements of structure, catalysis and control. The conflict between the requirement of structural stability and the requirement of functional specificity and efficiency, under varying environmental conditions in which they are often called upon to function, has been evolutionarily solved by a process of thermodynamic compensation. In the simplest form of thermodynamic compensation the Gibb's free energy change (delta G) of a process occurring under different environmental conditions is kept constant (linear compensation) or allowed to vary slightly (non linear compensation) by compensating a large change in enthalpy (delta H) by an equally (or nearly 80) large change in entropy, delta S. In processes like protein adsorption to surfaces the number of various types of interactions involved is so large that compensatory or augmenting changes in the same type of thermodynamic parameter may occur and complicate the picture. Published data do, however, suggested the occurrence of thermodynamic compensation in protein adsorption. It is pointed out that the simultaneous measurement of two thermodynamic parameters, namely, enthalpy change (delta H), and heat capacity change (delta Cp), under appropriate conditions could often lead to an understanding of the dominant types of forces involved in adsorption.

Chain length dependency of fatty acid and carbamate binding to serum albumin

The binding interactions of bovine serum albumin (BSA) with the unbranched fatty acids (FA) pentanoate (five-carbon chain length: C5) up to nonanoate (C9), and the carbamates n-methyl carbamate (equivalent to C3) up to n-hexyl carbamate (equivalent to C8) were examined using an ultrafiltration technique. A single, high-affinity site was observed for each of the FA, with an increasing number of secondary sites with increasing chain length. From binding affinity and competition data, there appear to be distinct albumin sites for the short-chain (less than or equal to C7) and the medium-chain (greater than or equal to C8) FA. Published data suggest that the medium-chain FA site is one of the major drug-binding sites on human serum albumin (HSA) or BSA, the indole/benzodiazepine site. Competition between the FA and warfarin for BSA or HSA binding was studied by ultrafiltration and fluorescence methods and suggests that the short-chain FA site may lie in the same region as a second major drug-binding site, the large warfarin-binding area. Thermodynamic parameters of the FA-BSA interactions are suggestive of primary binding being a combination of electrostatic and hydrophobic binding and secondary binding being purely hydrophobic in nature. Carbamate interactions with BSA show several primary sites and also suggest a disparity between the binding of ligands of less than or equal to 7 and greater than or equal to 8 in total length, but there was no evidence of competition between FA and carbamates. A model is proposed to explain these observations, which includes the suggestion that several classes of hydrophobic binding areas exist, each of which is specific for ligands of a restricted range of chain lengths.

Interactions of some phenylindanedione anticoagulants with human serum albumin

This study enabled us, to define the quantitative parameters of the interactions which give rise to the formation of complexes between five phenylindanediones and albumin or polymethacryate. The existence of three attachment sites were demonstrated, by which these ligands are bound to the macromolecule. The results from the thermodynamic study of this phenomenon, together with the information supplied by; various spectroscopic methods; the formation of a complex between a synthetic polymer carrying amine functions, and the study of ligands in the presence of surfactant, were all in agreement. Furthermore, a significant correlation between the association constant and physiochemical parameters lipophilic character and acidity was obtained, leading to the conclusion that; the interactions permitting the formation of the complexes between albumin and the five anionic ligands seem to be principally hydrophobic and, to a lesser degree, electrostatic. The latter only occurred in a particular medium at sites which were mainly hydrophobic.

Malaria, quinine and red cell lysis

An hypothesis is presented to explain the red cell lysis which accompanies an acute malarial infection, as well as the mode of action of certain schizonticidal drugs in the quinoline and acridine series. Quinine and a number of other antimalarial drugs have been found to counteract the inhibition by protein of fatty acid-induced lysis, when tested in an in vitro system. It is suggested that these schizonticides exert their chemotherapeutic effect by inducing the premature lysis of the parasitized red cell, as a result of relieving the inhibition by protein of haemolysis.