Blood Protein Binding Research Articles

Blood-to-brain transfer of various oxicams: effects of plasma binding on their brain delivery.

The objective of this work was to assess the influence of binding to plasma proteins and to serum on the brain extraction of four antiinflammatory oxicams. The brain extraction of isoxicam, tenoxicam, meloxicam and piroxicam was investigated in rats using the carotid injection technique. Blood protein binding parameters were determined by equilibrium dialysis using human serum, human serum albumin (HSA) and alpha-l-acid glycoprotein (AAG) solutions at various concentrations. All oxicams had low values of brain extraction, between 19% and 39% when dissolved in serum, i.e. under physiological conditions. Brain efflux rate constants calculated from the wash-out curves were the same in the absence or presence of serum. Brain efflux was inversely related to the polarity of the oxicams, such that the higher their H-bonding capacity, the lower their brain efflux. The free dialyzable drug fraction was inversely related to protein concentration. However, rat brain extraction was always higher than expected from in vitro measurements of the dialyzable fraction. Except for piroxicam whose brain extraction was partially decreased in the presence of proteins, the serum unbound and initially bound fractions of oxicams both seem available for transfer into the brain. Modest affinities for AAG rule out any related effect. More surprising is the apparent lack of effect on brain transfer of the high-affinity binding to HSA and serum. The enhanced brain uptake of meloxicam in the presence of AAG could be a result of interactions between this globular protein and the endothelial wall.

Inhalation toxicokinetics of butoxyethanol and its metabolite butoxyacetic acid in the male Sprague-Dawley rat.

A total of 16 male Sprague-Dawley rats were continuously exposed to 20 ppm or 100 ppm butoxyethanol (BE) vapor for 1, 2, 3, 4, 6, 8, 10, or 12 days. Urine was collected in 24-h intervals and stored at -70 degrees C. At the end of the exposure the animals were euthanized by decapitation and tissue samples of blood, muscle, liver and were rapidly collected and frozen to -70 degrees C. The samples were later derivatized and analyzed for BE and its major metabolite butoxyacetic acid (BAA) by electron capture gas chromatography. BE and BAA were rapidly distributed to the tissues examined. The concentration of BE in blood was slightly higher, and that of BAA markedly higher than in other tissues, indicating weak (BE) and pronounced (BAA) blood protein binding, respectively. BE was efficiently metabolized and the blood clearance averaged 2.6 l/h per kg, corresponding to a hepatic extraction ratio of about 0.75. The renal clearance of BAA (average 0.53 l/h per kg) corresponded to approximately 15% of the renal blood flow. The kinetics of BE and BAA were linear up to 100 ppm. There were no clear indications of changes in the toxicokinetics, such as metabolic induction or inhibition of metabolism or excretion, during the course of the exposure. The recovery of BAA in urine was 64% of the calculated inhaled amount of BE, on an equimolar basis.

A dialogue on analogues Newer vitamin-D drugs for use in bone disease, psoriasis, and cancer

Many new analogues of the vitamin-D hormone, 1 α,25-dihydroxy-vitamin D 3 [1 α,25-(OH) 2D 3; calcitriol], have emerged that can mimic its various actions in classic calcium transport systems and/or in the regulation of cell proliferation and cell differentiation. Though some of these analogues have accentuated activity in cell differentiation assays in vitro, they lack appreciable “calcemic” activity in vivo, leading to the name “noncalcemic analogues.” Several of these analogues are promising candidates for use in treatment of psoriasis and in tumor suppression, one of them, calcipotriol, being already widely approved for the former indication. New generations of calcemic analogues with altered pharmacokinetics are appearing for use in secondary hyperparathyroidism and osteoporosis. We believe that the selective properties of both types of analogues stem from altered receptor binding, blood protein binding, and rate of catabolism.

Axial tissue diffusion can account for the disparity between current models of hepatic elimination for lipophilic drugs.

An assumption of previous models of hepatic elimination is that there is negligible axial diffusion in the liver. We show, by construction of a stochastic model and analysis of published data, that compounds which are readily diffusible and partitioned into hepatocytes may undergo axial tissue diffusion. The compounds most likely to be affected by axial tissue diffusion are the lipophilic drugs for which the cell membranes provide little resistance and which are highly extracted, thereby creating steep concentration gradients along the sinusoid at steady state. This phenomenon greatly modifies the availability of the compound under conditions of altered hepatic blood flow and protein binding. For moderately diffusible compounds, these relationships are similar to those predicted by the simplistic venous-equilibrium model. Hence, the paradoxical ability of the venous-equilibrium model to describe the steady-state kinetics of lipophilic drugs such as lidocaine, meperidine, and propranolol may be finally resolved. The effects of axial tissue diffusion and vascular dispersion on hepatic availability of drugs are compared. Vascular dispersion is of major importance to the availability of poorly diffusible compounds, whereas axial tissue diffusion becomes increasingly dominant for highly diffusive and partitioned substances.

Selective in vivo tumor localization of heptacar☐ylic porphyrin isomer I in a bladder tumor model: a novel technique to modulate porphyrin localization

We were the first to report that uroporphyrin isomer I is a superior tumor localizer when compared with hematoporphyrin derivative. In the present study, we have examined the tumor localization of heptacar☐ylic porphyrin isomer I (hepta-P) using a bladder tumor model. We have also compared it to that found with uroporphyrin isomer I (Uro-P). We now show, for the first time, that (hepta-P) isomer I can be selectively retained in bladder malignant cells, a novel observation which has not yet been described by other investigators. Furthermore, we have provided a novel technique to modulate and manipulate blood protein binding to porphyrin in a controlled manner, such that the tumor localization properties can be effectively utilized without prolonged retention in the skin and to produce high uptake in the tumor, i.e., a higher therapeutic ratio. The biodistribution of hepta-P in different organs is presented.

Pharmacokinetics and pharmacodynamics in critically ill patients.

AbstractThe rapidly changing physiology of critically ill patients causes variations in the absorption, distribution, metabolism, excretion, and pharmacodynamic effect of drugs used to treat these patients. Alterations in fluid status, cardiac, renal and hepatic function, and circulating serum proteins necessitate increased attention to drug selection and dosage modification. Cardiac failure results in decreased absorption, metabolism, and excretion of drugs while renal failure results in parent drug and metabolite accumulation, increases in unbound drug, and changes in distribution volume. The changes in hepatic blood flow and protein binding, and decreases in hepatocellular mass and enzyme function that occur in hepatic failure may alter the clearance of several drugs. Serum drug concentrations are helpful in defining the pharmacokinetics and ultimately the pharmacodynamic effect of the drugs used in critically ill patients. The serum drug concentrations must be interpreted in association with their pharmacodynamic effect and the clinical situation. Adjusting drug therapy based on pharmacokinetic principles is discussed in detail with specific suggestions for dosage modifications in renal and hepatic failure.

Blood protein binding of cyclosporine in transplant patients.

The objective of this study was to compare the binding of cyclosporine to blood proteins between four healthy subjects and five liver and eight renal transplant patients. Fresh heparinized blood was obtained, to which sufficient quantities of tritium-labelled cyclosporine and unlabelled cyclosporine were added to blood samples or red blood cell (RBC) suspensions. Concentrations of cyclosporine in whole blood, plasma, RBC suspension, and phosphate buffer were estimated by liquid scintigraphy. The blood:plasma ratio of cyclosporine in transplant patients was significantly lower (P less than .05) than that in healthy volunteers. The RBC:buffer ratio, a measure of affinity of RBCs for cyclosporine, was highest in those with liver transplants and lowest in those with kidney transplants. The unbound fraction of cyclosporine in plasma was less in transplant patients than in healthy volunteers. The results of this study indicate that there are differences in blood protein binding of cyclosporine between transplant patients that may contribute to the differences in the pharmacokinetics and pharmacodynamics of this drug.

Binding of 2-amino-3-methylimidazo[4,5-f]quinoline to hemoglobin and albumin in vivo in the rat. Identification of an adduct suitable for dosimetry.

Blood protein binding by the food-borne carcinogen 2-amino-3-methylimidazo[4,5-f]quinoline (IQ) was investigated using male Sprague-Dawley rats. Among the many blood proteins modified in rats dosed intragastrically with [3H(G)]IQ, hemoglobin and albumin were modified in a dose dependent fashion. Albumin bound 3-5 times more IQ than hemoglobin at doses from 2 to 150 mumol. IQ-modified serum albumin was enzymatically digested using Pronase and analyzed by h.p.l.c. Many peptide fragments containing radioactivity were detected but the low level of protein modification (0.01-0.04% of dose) prevented spectroscopic analyses of these adducts. An in vitro system containing hepatic microsomes metabolized IQ to a reactive species which could bind to serum albumin. One major adduct was formed at the cysteine residue using this activation system and was identical to an adduct isolated from in vivo-modified albumin. Chemical and spectroscopic analyses of the Pronase fragment proved the adduct was a tripeptide containing N2-cysteinesulfinyl-IQ. A chemically identical adduct was formed in vitro when N-hydroxy-IQ was incubated with serum albumin. As much as 10% of the IQ bound to serum albumin in vivo was present as this sulfur-linked adduct based on h.p.l.c. analysis of the Pronase digest fragments and on the acid-labile activity which could be recovered as IQ.

1 - The Fate of Drugs in Pregnancy

The response of mother and fetus/neonate to drugs administered to the pregnant woman is determined largely by drug disposition and elimination within and between mother and fetus. Physiological changes occurring in pregnancy may result in reduced plasma protein binding, an increase in the apparent volume of distribution, and more rapid metabolic and renal clearance of certain drugs than are usually found in non-pregnant women. The consequences are relevant for the peak concentration of drug achieved after a single dose, the half-life of the drug, and the drug concentration to which the fetus is exposed via the placenta. Drugs whose dosage may need to be altered in pregnancy include most anticonvulsants, lithium, digoxin, certain beta-blockers, ampicillin and cefuroxime; for drugs which have not been specifically investigated, no generalizations are possible. Very few drugs given in pregnancy fail to cross the placenta and, as a rule, drug molecules not bound to plasma protein diffuse along a concentration gradient to establish and maintain an equilibrium. Because movement of drug molecules is bidirectional, the placenta is the main portal of exit from, as well as entry to, the fetus. The pharmacological response of the fetus to drugs which it receives depends mainly on the unbound concentration of drug in fetal blood--unwanted effects seldom occur if the maternal dose is correct; exceptions include tetracycline, antithyroid drugs, coumarin anticoagulants, aspirin, indomethacin and cerebral depressant drugs (opiates, barbiturates and phenothiazines). The total (bound plus unbound) drug concentration on the fetal side of the placenta is usually lower than on the maternal side except where differences in blood pH and/or protein binding lead to 'trapping' of drug in the fetus; the latter phenomenon may prove hazardous after birth because of the neonate's limited capacity to eliminate drugs by metabolism and excretion.

Electrochemical Chromatographic Determinations of Morphine Antagonists in Biological Fluids, with Applications

The morphine antagonists naltrexone and naloxone were extracted from plasma and urine, separated on a chromatographic column, and assayed by electrochemical detection. Optimum oxidation potentials were 0.65 V for morphine and 0.75 V for naloxone and naltrexone. Assay sensitivities were 2–5 ng/mL for plasma and 10 ng/mL for urine. The assays were applied to determine red blood cell partition coefficients of 1.83 ± 0.15 (SD) for naltrexone and 1.49 ± 0.27 (SD) for naloxone in a concentration range of 10-3500 ng/mL. No significant time dependence for the partitioning could be observed. Plasma protein binding in the same concentration range, determined by ultracentrifugation, was 27.7% ± 2.5% (SD) for naltrexone and 30.1% ± 5.1% (SD) for naloxone. The degree of protein binding did not change in the presence of morphine for morphine-antagonist ratios between 1:10 and 10:1. No concentration dependencies of red blood cell partitioning or protein binding were observed.

Hepatic disease and drug pharmacokinetics.

Recent clinical investigations and reports of theoretical models have provided considerable insight into mechanisms of hepatic drug elimination and into derangements that may occur in drug absorption and disposition in patients with hepatic disease. Carefully conducted and well controlled clinical studies have demonstrated that hepatic disease may alter substantially one or more pharmacokinetic parameters of drug absorption and disposition. Physiological models of hepatic drug elimination have emphasised the importance of physiological variables such as hepatic blood flow, protein binding and intrinsic clearance of the liver on hepatic drug elimination. Both clinical investigations and theoretical considerations have indicated that the influence of hepatic disease on the pharmacokinetics of a drug may be complex and may result in either unchanged, retarded or even accelerated drug elimination. Changes in response to drugs in patients with hepatic impairment add to this complexity. Although general guidelines may be formulated now to assist clinicians in constructing dosage regimens of several important drug classes (notably the benzodiazepines and barbiturates) in hepatic disease, it is not now possible to predict in an individual the influence of a specific hepatic disease on the disposition of a drug, with the exception that the oral availability of drugs with high hepatic extraction ratios is increased in patients with cirrhosis and protacaval shunting of blood. Attempts to correlate concentrations of endogenous substances (such as bilirubin), or the pharmacokinetics of model drugs (such as antipyrine), with the pharmacokinetics of drugs that are useful in patients with hepatic impairment have not resulted in clinically useful tests of hepatic drug elimination. Following the administration of a drug to a patient with hepatic impairment, careful monitoring of the patient and also monitoring of plasma or blood drug concentrations remain important considerations.

Sulfate and glucosamine labelling of the intercellular matrix in vitellogenic follicels of a moth.

InHyalophora cecropia the intercellular spaces of the follicles contain during vitellogenesis a matrix that can be labelled eitherin situ or in culture with35S-sulfate and3H-glucosamine. The matrix was demonstrated by autoradiography and also by treating follicles for 15 min with pronase, which released TCA-soluble matrix fragments with molecular weights of up to 2×106 daltons. Testicular hyaluronidase degraded the high molecular weight fragments, and thus it is probable that they are chondroitin sulfate-like mucopolysaccharides. With the termination of vitellogenesis new matrix is no longer deposited, and the pre-existing material is disassembled. The sulfated matrix may account for the patency of the intercellular diffusion channels essential for blood protein uptake and also for the low level, extracellular binding of blood proteins that characterizes the vitellogenic follicle inHyalophora.

Extracellular concentrating of proteins in the cecropia moth follicle.

AbstractYolk proteins, derived from the blood, are incorporated into the oocytes of insects and certain vertebrates by pinocytosis, but reach the oocyte surface only after penetrating the surrounding follicular epithelium via intercellular channels. In an investigation of the events occurring in these intrafollicular spaces, the dense extracellular material present between the follicle cells and in the oocyte's brush border was extracted from vitellogenic cecropia moth follicles by soaking in physiological saline. Quantitative immunochemical determination of several eluted blood proteins revealed that these components had been more concentrated in the extracellular spaces than in the blood. The average concentration factors were 2.5 for the predominant yolk protein, vitellogenin, and 4.5 for the carotenoid protein.Since injected foreign proteins were also accumulated in the spaces, the concentrating mechanism seemed to act on all available proteins. However, in vitro inhibition of yolk formation with dinitrophenol resulted in a selective increase in the amount of extracellular vitellogenin in follicles which had been previously exposed to a medium low in this protein, suggesting accumulation of a factor with a specific affinity for it. Furthermore under certain conditions vitellogenin was more readily released from the concentrate than was the carotenoid protein. These results indicate that, despite apparent lack of discrimination in the binding of blood proteins in the spaces, extracellular interactions may contribute to the selectivity known to occur during vitellogenesis.