Leucocyte-associated plasma proteins in leucocytes during disease states, and in leukaemic cells

Seventy-Five Years of Research on Protein Binding

This review summarizes evidence that the impact of protein binding of the activity of antibiotics is multifaceted and more complex than indicated by the numerical value of protein binding alone. A plethora of studies has proven that protein binding of antibiotics matters, as the free fraction only is antibacterially active and governs pharmacokinetics. Several studies have indicated that independent from protein binding of immunoglobulin G, albumin, α1-acid-glycoprotein, and pulmonary surfactant acted synergistically with antibacterial agents, thus suggesting that some intrinsic properties of serum proteins may have mediated serum-antibiotic synergisms. It has been demonstrated that IgG and albumin permeabilized Gram-negative and Gram-positive bacteria and facilitated the uptake of poorly penetrating antibiotics. Alpha-1-acid-glycoprotein and pulmonary surfactant also exerted a permeabilizing activity, but proof that this property results in a sensitizing effect is missing. The permeabilizing effect of serum proteins may explain why serum-antibiotic synergisms do not represent a general phenomenon but are limited to specific drug-bug associations only. Although evidence has been generated to support the hypothesis that native serum proteins interact synergistically with antibiotics, systematic and well-controlled studies have to be performed to substantiate this phenomenon. The interactions between serum proteins and bacterial surfaces are driven by physicochemical forces. However, preparative techniques, storage conditions, and incubation methods have a significant impact on the intrinsic activities of these serum proteins affecting serum-antibiotic synergisms, so these techniques have to be standardized; otherwise, contradictory data or even artifacts will be generated.

A molecular functional study on the interactions of drugs with plasma proteins

The binding of drugs to plasma proteins, such as albumin and alpha1-acid glycoprotein (AGP) is a major determinant in the disposition of drugs. A topology analysis of drug binding sites on HSA and AGP was determined using various methods, including spectroscopy, QSAR, photoaffinity labeling and site directed mutagenesis. Recombinant albumin was found to be useful for rapidly identifying drug binding sites. The binding sites on AGP are not completely separated but are partially overlapped, and Trp, Tyr, Lys and His residues in the drug binding pockets play important roles in this process. Drug displacement is somewhat complex, due to the involvement of multiple effects. The reduced binding in uremic patients may be explained by a mechanism that involves a combination of direct displacement by free fatty acids as well as cascade effects of free fatty acids and unbound uremic toxins for significant inhibition in serum binding. Albumin-containing dialysate is useful for the extracorporeal removal of endogenous toxins and in the treatment of drug overdoses. Oxidized albumin is a useful biomarker for the quantitative and qualitative evaluation of oxidative stress. Interestingly, AGP undergoes a structural transition to a unique structure that differs from the native and denatured states, when it interacts with membranes.

Structural and drug-binding properties of alpha(1)-acid glycoprotein in reverse micelles

Alpha(1)-acid glycoprotein (AGP) is a glycoprotein that consists of 183 amino acid residues and five carbohydrate chains and binds to neutral and basic drugs. We examined the structural properties and ligand-binding capacity of AGP in interactions with reverse micelles. Also, detailed information was obtained by comparing several different states of AGP. Interaction with reverse micelles induced a unique conformational transition (beta-sheet to alpha-helices) in AGP and decreased the binding capacity for the basic drug, chlorpromazine and the steroid hormone, progesterone to AGP. These structural conformations are very similar to those observed under conditions of acidity and high ionic strength (pH 2.0, 1.5 M NaCl). This structure seems to be an intermediate between the native state and the denatured state, possibly a molten globule. The present results suggest that when AGP interacts with the biomembrane, it undergoes a structural transition to a unique structure that differs from the native and denatured states and has a reduced ligand-binding capacity.

Correlation between leukocyte-associated plasma proteins and white cell differential count

Prealbumin, albumin, orosomucoid (including the cellular variant orosomucoid2), alpha 1-antitrypsin, haptoglobin and transferrin were quantified in 107 cell samples from acute and chronic myeloid leukaemia, seven polycytaemia, seven normal blood marrow and 56 normal blood leukocytes by crossed immunoelectrophoresis. By statistical multivariate analyses, the individual plasma proteins and their combined protein patterns were correlated with the diagnoses and it was demonstrated that acute leukaemia cell samples contained significantly different protein patterns compared with the other diagnostic groups and normal controls. By comparison with the white blood cell differential count, in 78 samples of acute leukaemia, it was demonstrated that the protein patterns were significantly correlated with the specific cell types in the samples. In all, the differential counts accounted for about 29% of the variation in protein patterns. Alpha 1-antitrypsin was found significantly correlated with the myeloblasts and myelo-band cells. Orosomucoid2 and haptoglobin were significantly correlated with mature granulocytes and albumin was significantly correlated with lymphocytes. In some cell samples, after cytotoxic treatment of acute leukaemia, the granulocytes did not have orosomucoid2 despite normal morphology, suggesting defective maturation of these granulocytes. These results indicate that the mechanisms responsible for uptake of plasma proteins are highly specific for different cell types and in the case of myeloid cells specifically related to cell differentiation.

The importance of granulocyte elastase in haematological diagnosis

PMN elastase is a useful additional parameter in the differential diagnosis of the leukaemias. In all patients with myelocytic leukaemias there were elevated levels of elastase-alpha 1-proteinase inhibitor (E-alpha 1PI), while in the lymphatic leukaemias complexed elastase levels were decreased. The highest values were found in the peripheral blood plasma and bone marrow plasma of patients with CML. Despite high E-alpha 1PI concentrations there were no signs of bleeding or consumption of plasmatic coagulation factors. In AML a wide range of E-alpha 1PI levels was observed, extending from slightly elevated to four hundred-fold increased. In myeloblastic leukaemias without maturation (FAB M 1) the concentrations of complexed elastase remained below 150 ng/ml. In myeloblastic leukaemias with maturation (FAB M2) the E-alpha 1PI values ranged between 214 ng/ml and 850 ng/ml (means = 402 +/- 69), and in myelo-monoblastic leukaemias (FAB M4) between 450 ng/ml and 720 ng/ml (means = 663 +/- 72). The only case of promyelocytic leukaemia (FAB M 3) exhibited an extremely high value of 4,550 ng/ml, while a monocytic leukaemia (FAB M5) showed an extremely low value of 5 ng/ml. During cytostatic therapy there was a rapid decrease in levels of complexed elastase, with E-alpha 1PI values returning to normal in remission. In recidivating cases there was an increase of E-alpha 1PI levels in AML and a decrease in ALL. There was a correlation between the E-alpha 1PI concentrations in peripheral plasma and leukaemic bone marrow infiltration, so providing a good basis for monitoring remission from leukaemia and indicating relapse. It was also interesting to observe an extremely low E-alpha 1PI level (5 ng/ml) in patients with myelodysplasia. Under Decortin/Plenastril therapy the concentration rose to 50 ng/ml. An E-alpha 1PI level of 10 ng per ml was observed in one case of Ranitidine agranulocytosis. Under corticoid therapy the value returned to normal within eight days.

Expression of the alpha-1-antitrypsin gene in mononuclear phagocytes of normal and alpha-1-antitrypsin-deficient individuals

To evaluate the contribution of mononuclear phagocytes, and particularly alveolar macrophages, to alpha-1-antitrypsin (alpha 1AT) production in normal and alpha 1AT-deficient individuals, Northern analysis with a human alpha 1AT complementary DNA was used to demonstrate that alpha 1AT messenger RNA (mRNA) can be detected in liver, blood monocytes, and alveolar macrophages. Quantification of alpha 1AT mRNA expression demonstrated that: (a) type PiMM monocytes and alveolar macrophages expressed, respectively, 200-fold and 70-fold less alpha 1AT mRNA per cell than the liver; (b) the level of expression of the alpha 1AT gene was increased during the in vitro maturation of blood monocytes; and (c) blood monocyte and alveolar macrophage levels of expression of the alpha 1AT gene were the same in PiMM and PiZZ individuals. However, the amount of newly synthesized alpha 1AT secreted by ZZ alveolar macrophages was 10 times lower than that secreted by MM alveolar macrophages. Thus, mononuclear phagocytes of PiZZ individuals express a secretory defect in alpha 1AT in a fashion similar to hepatocytes. Not only do mononuclear phagocytes provide a readily accessible cell to evaluate the regulation of alpha 1AT gene expression, but these cells may contribute to the levels of alpha 1AT present in the lower respiratory tract in the normal and ZZ states.