Influence of propofol concentration in human plasma on free fraction of the drug

Drugs exist in blood in two forms: free and bound to proteins and blood cells. It is generally assumed that only the unbound form of a drug exerts pharmacological activity as it is able to diffuse across the membranes and reach the site of action. Since for the majority of drugs their free fraction is usually constant, the therapeutic effect of the drug is most often correlated with its total concentration. However, in case of some disease states (e.g. renal or hepatic disorders) the protein concentration may change dramatically, resulting in clinically significant change of free drug fraction. The results presented in the paper prove that, in case of propofol, an increase of free fraction occurs with a decrease of total drug concentration. This dependence is observed both in vitro (in artificial and native human plasma) and in vivo. Free propofol fraction, which in clinical conditions ranges from 1 to 3%, at very low total propofol concentrations (below 0.01 microgml(-1)) tends to reach 100%. This increase of free drug percentage is discussed in terms of its possible reasons as well as its potential clinical relevance.     

Determination of amphotericin B, liposomal amphotericin B, and amphotericin B colloidal dispersion in plasma by high-performance liquid chromatography

Amphotericin B is a potent polyene antifungal drug for intravenous treatment of severe infections. It is used as amphotericin B-deoxycholate and in order to reduce amphotericin B toxicity as lipid-formulated complex (liposomal or colloidal dispersion). A sensitive and specific analytical method is presented for the separation of lipid-complexed and plasma protein-bound amphotericin B in human heparinized plasma. This separation, which is required for pharmacokinetic studies, is achieved by solid-phase extraction (SPE) via Bond Elut C₁₈. The protein-bound amphotericin B has a higher affinity to the SPE material and is therefore retained, whereas the lipid-complexed amphotericin B is eluted in the first step. The recovery of the SPE was >75% for high concentrations and >95% for low concentrations. Quantification was performed by reversed-phase HPLC using a LiChrosorb-RP-8 column, UV detection (λ=405 nm) and a mixture of acetonitrile–methanol–0.010 M NaH₂PO₄ buffer (41:10:49, v/v) as mobile phase. The retention time for amphotericin B under the given conditions was 6.7 min. The calibration curves were found to be linear (r≥0.999) in two different ranges (5.0–0.50 μg/ml and 0.50–0.005 μg/ml). Intra- and inter-day precision and accuracy fulfilled the international requirements. No interference from other drugs (typical broad medication for intensive-care patients) or common plasma components was detected in >400 samples analyzed.     

Absence of genetic polymorphism of human plasma fibronectin studied by immunoelectrophoresis

Plasma fibronectin from 500 blood donors was studied by immunoelectrophoresis. No variants were found. Plasma fibronectin does not appear to be electrophoretically polymorphic in humans.     

Absence of generation of oxygen-containing free radicals with 4'-deoxydoxorubicin, a non-cardiotoxic anthracycline drug

In vitro ESR studies of doxorubicin and 4'-deoxydoxorubicin have been conducted using the spin traps PBN and DMPO. Solutions prepared in the presence of atmospheric oxygen at pH = 12 exhibited a typical semiquinone signal preceded by a short-lived signal attributed to perhydroxyl radical, HO2. At physiological pH the perhydroxyl signal was observed in the doxorubicin solution but not in 4'-deoxydoxorubicin. In the absence of oxygen, at pH = 7.5, neither drug exhibited a signal. A relationship is proposed between the perhydroxyl radical and the cardiotoxicity observed in doxorubicin but not in 4'-deoxydoxorubicin.     

Presence of lorazepam in the blood plasma of drug free rats

Lorazepam has been identified in the blood plasma of non-medicated rats by means of HPLC and gas chromatography combined with mass spectrometry. It was found to be present in about 1 ng per ml blood plasma. This pharmacologically highly active compound is the first dichlorinated benzodiazepine described to occur naturally in a tissue of mammals, not treated with benzodiazepines.     

Conformational changes in human prothrombin as detected by antibody populations

The amino-terminal peptides of human prothrombin corresponding to residues 1-51 and 52-156 have been isolated from a thrombin digest of prothrombin fragment 1. The products of digestion were purified by means of barium citrate and ammonium sulfate precipitations, followed by gel filtration and hydroxyapatite chromatographies. They were identified by their molecular sizes as well as their amino acid compositions. Peptides 1-51 (F1A) and 52-156 (F1B) were used as affinity ligands for the isolation of antibody populations from antisera that were elicited against human prothrombin or prothrombin fragment 1. These antibody populations displayed restricted specificity for the respective ligands as shown by competitive radioimmunoassays. They were used to study the conformational changes in prothrombin and fragment 1. The F1A-specific antibody populations detected a conformational change which is stabilized by calcium ions and which has a transition midpoint at approximately 0.2 mM calcium ion concentration. The F1B-specific antibody populations identified a different conformational change which is destabilized by calcium ions and which has a transition midpoint at approximately 0.5 mM calcium.     

Determination of cimetidine in human plasma by free capillary zone electrophoresis

The separation of cimetidine from the metabolites cimetidine amide and cimetidine sulfoxide, endogenous creatinine and the internal standard ranitidine was achieved by capillary electrophoresis in less than 5 min. All compounds were well separated from cimetidine, including possible plasma ingredients, as the UV spectra of cimetidine standard and cimetidine from the plasma extract match. Plasma levels of cimetidine were determined in the range 250–3000 ng/ml in plasma and higher concentrations were determined by dilution of the sample with blank plasma.     

Flexibility in monomeric Cu,Zn superoxide dismutase detected by limited proteolysis and molecular dynamics simulation

Limited proteolysis by trypsin of monomeric Cu,Zn superoxide dismutase from Escherichia coli induces a specific cleavage of the polypeptide chain at the level of Lys60 located in the S-S subloop of loop 6,5 where, when compared to the eukaryotic enzyme, a seven-residues insertion, completely exposed to the solvent, is observed. This result suggests that this subloop is disordered and flexible, thus enabling binding and adaptation to the active site of the proteolytic enzyme. Indeed, molecular dynamics simulation indicates that the S-S subloop undergoes high fluctuations and that its high flexibility coupled to an high solvent accessibility can explain the specific bond selection of the protease. As a matter of fact, of the possible 14 solvent accessible proteolytic sites only the Lys60 flexible site is cleaved. High flexibility and solvent exposure are confirmed by the short water residence time for the residues corresponding to the cleavage site evaluated by molecular dynamics simulation. These experiments demonstrate that molecular dynamics simulation and limited proteolysis are complementary and unambiguous tools to identify flexible sites in proteins.     

Absence of effect of estrogen on dopamine, norepinephrine and beta-endorphin-like immunoreactivity in human plasma

The plasma concentrations of immunoreactive norepinephrine (NE), dopamine (DA), beta-endorphin (beta-E), luteinizing hormone (LH) and follicle stimulating hormone (FSH) were determined by RIA and HPLC every 6 h until 72 h after iv administration of conjugated estrogens during the midfollicular phase. The LH level showed a biphasic pattern after the injection of conjugated estrogens, i.e. significant suppression (-50%) for 6-42 h after the injection, followed by a rebound increase with a peak (+85%) at 72 h. The plasma levels of immunoreactive beta-E, NE and DA did not change significantly for 72 h after the injection.     

Metabolism of low-density lipoprotein free cholesterol by human plasma lecithin-cholesterol acyltransferase

The metabolism of cholesterol derived from [3H]cholesterol-labeled low-density lipoprotein (LDL) was determined in human blood plasma. LDL-derived free cholesterol first appeared in large alpha-migrating HDL (HDL2) and was then transferred to small alpha-HDL (HDL3) for esterification. The major part of such esters was retained within HDL of increasing size in the course of lecithin-cholesterol acyltransferase (LCAT) activity; the balance was recovered in LDL. Transfer of preformed cholesteryl esters within HDL contributed little to the labeled cholesteryl ester accumulating in HDL2. When cholesterol for esterification was derived instead from cell membranes, a significantly smaller proportion of this cholesteryl ester was subsequently recovered in LDL. These data suggest compartmentation of cholesteryl esters within plasma that have been formed from cell membrane or LDL free cholesterol, and the role for HDL2 as a relatively unreactive sink for LCAT-derived cholesteryl esters.     

Determination of anti-HIV drug concentration in human plasma by MALDI-TOF/TOF

The antiretroviral therapeutic drug monitoring is becoming increased in clinical care to determine the best dosage regimen adapted to each patient. Here, the determination of the anti-HIV drugs lamivudine, lopinavir, and ritonavir concentration in the plasma of HIV-infected patients by MALDI-TOF/TOF is reported. The volume of the plasma sample was 600 microL. Plasma samples were extracted by solid-phase (divinylbenzene and N-vinylpyrrolidone) and evaporated in a water bath under a nitrogen stream. The extracted samples were reconstituted with methanol (100 microL), mixed (1:1) with a saturated matrix solution (4-hydroxybenzoic acid in 50% acetonitrile-0.1% trifluoracetic acid), and spotted onto the MALDI-TOF/TOF sample target plate. The lamivudine, lopinavir and ritonavir concentration was determined by standard additions analysis. Regression of standard additions was linear over the anti-HIV drug concentration ranges explored (lamivudine, 0.010-1.0 pmol/microL; lopinavir and ritonavir, 0.0025-0.50 pmol/microL). Moreover, emtricitabine (i.e., the fluorinated analog of lamivudine) was used as the internal standard to determine the lamivudine concentration. The calibration curve was linear on the emtricitabine concentration ranging between 0.050 and 5.0 pmol/microL. The absolute recovery ranged between 80 and 110%. Values of the lamivudine, lopinavir and ritonavir concentration determined by MALDI-TOF/TOF are in excellent agreement with those obtained by HPLC-UV and HPLC-MS/MS. MALDI-TOF/TOF experiments allowed also the detection of the ritonavir metabolite R5. Zidovudine was undetectable by MALDI-TOF/TOF analysis because also the minimal laser intensity may induce the anti-HIV drug photolysis. The MALDI-TOF/TOF technique is useful to determine very low concentrations of anti-HIV drugs (0.0025-0.010 pmol/microL).     

Rapid quantitation of free fatty acids in human plasma by high-performance liquid chromatography

We report a rapid and sensitive method for separation and quantitation of free fatty acids (FFAs) in human plasma using high-performance liquid chromatography (HPLC). Two established techniques of lipid extraction were investigated and modified to achieve maximal FFA recovery in a reasonably short time period. A modified Dole extraction method exhibited greater recovery (90%) and short processing times (30 min) compared to the method of Miles et al. Reversed-phase HPLC using UV detection was used for plasma FFA separation and quantitation. Two phenacyl ester derivatives, phenacyl bromide and p-bromophenacyl bromide, were investigated in order to achieve optimal separation of individual plasma FFAs (saturated and unsaturated) with desirable detection limits. Different chromatographic parameters including column temperature, column type and elution profiles (isocratic and gradient) were tested to achieve optimal separation and recovery of fatty acids. Phenacyl bromide esters of plasma fatty acids were best resolved using an octadecylsilyl column with endcapped silanol groups. An isocratic elution method using acetonitrile–water (83:17) at 2 ml/min with UV detection at 242 nm and a column temperature of 45°C was found to optimally resolve the six major free fatty acids present in human plasma (myristic [14:0], palmitic [16:0], palmitoleic [16:1], stearic [18:0], oleic [18:1] and linoleic [18:2]), with a run time of less than 35 min and detection limits in the nmol range. The entire process including plasma extraction, pre-column derivatization, and HPLC quantitation can be completed in 90 min with plasma samples as small as 50 μl. Over a wide physiological range, plasma FFA concentrations determined using our HPLC method agree closely with measurements using established TLC–GC methods (r²≥0.95). In addition, by measuring [¹⁴C] or [³H] radioactivity in eluent fractions following HPLC separation of plasma FFA, this method can also quantitate rates of FFA turnover in vivo in human metabolic studies employing isotopic tracers of one or more fatty acids.     

Characterization of the multiple conformational States of free monomeric and trimeric human immunodeficiency virus envelope glycoproteins after fixation by cross-linker

The human immunodeficiency virus type 1 (HIV-1) gp120 exterior and gp41 transmembrane envelope glycoproteins assemble into trimers on the virus surface that represent potential targets for antibodies. Potent neutralizing antibodies bind the monomeric gp120 glycoprotein with small changes in entropy, whereas unusually large decreases in entropy accompany gp120 binding by soluble CD4 and less potent neutralizing antibodies. The high degree of conformational flexibility in the free gp120 molecule implied by these observations has been suggested to contribute to masking the trimer from antibodies that recognize the gp120 receptor-binding regions. Here we use cross-linking and recognition by antibodies to investigate the conformational states of gp120 monomers and soluble and cell surface forms of the trimeric HIV-1 envelope glycoproteins. The fraction of monomeric and trimeric envelope glycoproteins able to be recognized after fixation was inversely related to the entropic changes associated with ligand binding. In addition, fixation apparently limited the access of antibodies to the V3 loop and gp41-interactive surface of gp120 only in the context of trimeric envelope glycoproteins. The results support a model in which the unliganded monomeric and trimeric HIV-1 envelope glycoproteins sample several different conformations. Depletion of particular fixed conformations by antibodies allowed characterization of the relationships among the conformational states. Potent neutralizing antibodies recognize the greatest number of conformations and therefore can bind the virion envelope glycoproteins more rapidly and completely than weakly neutralizing antibodies. Thus, the conformational flexibility of the HIV-1 envelope glycoproteins creates thermodynamic and kinetic barriers to neutralization by antibodies directed against the receptor-binding regions of gp120.     

The expression of free oligosaccharides in human seminal plasma

Human seminal plasma is a complex mixture of proteins, glycoproteins, peptides, glycopeptides, and prostaglandins secreted by organs of the male reproductive tract. The components of this fluid have been implicated in the suppression of immune response, agonistic effects on sperm-egg binding, and promotion of successful implantation of the human embryo. Fractionation followed by biophysical analyses revealed that free oligosaccharides constitute a major component of the total glycoconjugates within seminal plasma. Significant findings of our analyses include the following: (i) the concentration of free oligosaccharides is 0.3-0.4 mg/ml; (ii) mono- and difucosylated forms of the disaccharide lactose are major components; (iii) many of the remaining oligosaccharides are also rich in fucose and carry Lewis(x) and/or Lewis(y) epitopes; (iv) a subset of the oligosaccharides express the reducing end sequence (GlcNAcbeta1-3/4Glc) not reported in human milk oligosaccharides; (v) oligosaccharides in seminal plasma exclusively express type 2 (Galbeta1-4GlcNAc) but not the type 1 sequences (Galbeta1-3GlcNAc) that predominate in human milk glycans; and (vi) the structural diversity of seminal plasma oligosaccharides is far less than human milk oligosaccharides. The agonistic effect of both fucose and fucosylated glycoconjugates on human sperm-egg binding in vitro suggests that fucosylated oligosaccharides may also promote fertilization in the female reproductive tract.     

Occurrence and distribution of glycoconjugates in human tissues as detected by the Erythrina cristagalli lectin

We applied a horseradish peroxidase-Erythrina cristagalli agglutinin (HRP-ECA) conjugate for histochemical staining of tissue sections from various formalin-fixed, paraffin-embedded human tissue specimens. The HRP-ECA conjugate showed broad reactivity, but there was a distinct distribution of native (not masked by sialic acid) and sialic acid-masked ECA binding sites in the various organs. Free ECA binding sites could be detected on red blood cells, lymphocytes of thymus, tonsil, lymph node, and in mucous substances of different organs. Independent of blood group type, the vascular endothelium exhibited strong ECA reactivity. Free ECA binding sites occurred in the cytoplasm of Kupffer's cells in liver, in histiocytic cells of thymus, lymph node, tonsil, and in bone marrow. Podocytes of kidney glomerulus, syncytiotrophoblasts of placenta, megakaryocytes in bone marrow, myelin sheath of nerve, medullary thymocytes, and hepatocytes, as well as islet cells of pancreas, contained only sialic acid-capped ECA binding sites. Inhibiting studies with galactose, lactose, and N-acetyl-lactosamine, as well as other sugars, revealed that this lectin is specific for galactosyl residues. In comparison to galactose and lactose, N-acetyl-lactosamine exhibited the highest inhibitory activity on lectin binding, supporting the concept that this lectin is most reactive with N-acetyl-lactosamine-type (type 2 chain) glycoconjugates.     

Determination of amphotericin B in human serum by liquid chromatography

A rapid reversed-phase high-performance liquid chromatographic method with a 30-mm long column is described for assaying amphotericin B in serum. After deproteinization of serum samples with methanol, the supernatant was injected onto a reversed-phase C₁₈ column, using 2.5 mM Na₂EDTA-acetonitrile (70:30, v/v) as the mobile phase. Amphotericin B was eluted at 1.5 min. Calibration plot of the peak area against concentration was linear from 0.05 to 25 μg/ml (C.V. of 3%). Within-day and day-to-day imprecision (C.V.) ranged between 1.33% and 3.61%. The application was evaluated in 55 serum samples from patients treated with amphotericin B.     

Genetic polymorphism in sheep plasma detected using antibodies to human plasminogen

Protein variation was identified in sheep when Western blots of polyacrylamide gels (routinely used to resolve transferrin polymorphism) were stained using antibodies to human plasminogen. The affinity of the antibodies to ovine plasma was less than 7% that of a human standard but they bound specifically to a single polymorphic protein. In 146 lambs and their parents the inheritance of the ovine plasminogen antigen polymorphism was consistent with four autosomal alleles segregating codominantly. However, an additional two lambs had types which were incompatible with their putative parents. The pedigrees of these lambs were tested by DNA fingerprinting and shown to have been incorrectly recorded. The genetic polymorphism detected by human plasminogen antiserum provided a probability of sire exclusion (PE) ranging from 0.04 to 0.32 and a polymorphic information content (PIC) of 0.08 to 0.50 in flocks of five sheep breeds: Perendale, Romney, Merino, Texel and Coopworth (in order of increasing genetic variation in this locus). Significant differences in allele frequency were observed between breeds but sampling did not assess the variation among flocks within a breed.     

Alterations in glomerular lectin binding sites of human kidney as detected by fluorescence microscopy

Summary Different lectins were used to study frozen sections of kidney samples showing alterations in routine immunofluorescence studies.Arachis hypogaea agglutinin (peanut lectin, PNA), lacking binding sites in normal glomeruli, bound to the glomeruli in two of the five samples studied, giving a granular fluorescence pattern. Concomitantly with the appearance of PNA-binding, binding sites for wheat germ agglutinin (WGA) appeared to be lost at glomeruli. Furthermore, changes in the expression of glomerular binding sites forWistaria floribunda (WFA),Helix pomatia (HPA) andDolichos biflorus (DBA) agglutinins could be seen in the kidneys studied, whereas the binding sites forUlex europaeus agglutin (UEA I) in vascular endothelia seemed to be unaltered.The results show that kidney specimens presenting changes in routine immunofluorescence studies may also present altered binding for certain lectins. On this basis we propose that certain lectins may aid in characterizing these changes and are thus of potential use in studying diseased kidneys.