Macrophage phagocytosis: analysis of particle binding and internalization

Imaging upregulated brain arachidonic acid metabolism in HIV-1 transgenic rats

Human immunodeficiency virus (HIV)-associated infection involves the entry of virus-bearing monocytes into the brain, followed by microglial activation, neuroinflammation, and upregulated arachidonic acid (AA) metabolism. The HIV-1 transgenic (Tg) rat, a noninfectious HIV-1 model, shows neurologic and behavioral abnormalities after 5 months of age. We hypothesized that brain AA metabolism would be elevated in older HIV-1 Tg rats in vivo. Arachidonic acid incorporation from the plasma into the brain of unanesthetized 7-to-9-month-old rats was imaged using quantitative autoradiography, after [1-(14)C]AA infusion. Brain phospholipase (PLA(2)) activities and eicosanoid concentrations were measured, and enzymes were localized by immunostaining. AA incorporation coefficients k* and rates J(in), measures of AA metabolism, were significantly higher in 69 of 81 brain regions in HIV-1 Tg than in control rats, as were activities of cytosolic (c)PLA(2)-IV, secretory (s)PLA(2), and calcium independent (i)PLA(2)-VI, as well as prostaglandin E(2) and leukotriene B(4) concentrations. Immunostaining of somatosensory cortex showed elevated cPLA(2)-IV, sPLA(2)-IIA, and cyclooxygenase-2 in neurons. Brain AA incorporation and other markers of AA metabolism are upregulated in HIV-1 Tg rats, in which neurologic changes and neuroinflammation have been reported. Positron emission tomography with [1-(11)C]AA could be used to test whether brain AA metabolism is upregulated in HIV-1-infected patients, in relation to cognitive and behavioral disturbances.

The potential role of phagocytic capacity in the osteolytic process induced by polyethylene wear particles

Osteolysis induced by ultra-high molecular weight polyethylene wear particles is the major cause of long-term failure of artificial joints. We examined the effects of wear particles on bioactivity by analysing the biophysical aspects of particle phagocytosis. We estimated the maximum number of internalized particles (the phagocytic capacity) for particles of various sizes and shapes. We demonstrated that elongated particles had a smaller phagocytic capacity than spherical particles of the same volume. A review of the literature showed that the ratio of particle concentration (number of particles/number of cells) to phagocytic capacity is critical for particle-induced biological responses. When this ratio was < 1, the biological response was approximately proportional to the ratio itself. When this ratio was > 1, limited changes in the biological response were observed. The saturation level of the phagocytic capacity for a particle population appears to reflect the degree of polyethylene particle-induced biological response.

Efflux of drugs and solutes from brain: the interactive roles of diffusional transcapillary transport, bulk flow and capillary transporters

We examined the roles of diffusion, convection and capillary transporters in solute removal from extracellular space (ECS) of the brain. Radiolabeled solutes (eight with passive distribution and four with capillary or cell transporters) were injected into the brains of rats (n=497) and multiple-time point experiments measured the amount remaining in brain as a function of time. For passively distributed compounds, there was a relationship between lipid:water solubility and total brain efflux:diffusional efflux, which dominated when k(p), the transcapillary efflux rate constant, was >10(0) h(-1); when 10(-1)<k(p)<10(-2) h(-1) both diffusion and convection contributed, and when k(p)<10(-3) h(-1), convective efflux dominated. Para-aminohippuric acid (PAH) experiments (n=112) showed that PAH entered the brain passively, but had efflux transporters. The total efflux rate constant, k(eff), was the sum of a passive component (k(p)=0.0018 h(-1)), a convective component (k(csf)=0.2 h(-1)), and a variable, concentration-dependent component (k(x)=0 to 0.45 h(-1)). Compounds with cell membrane transporters had longer clearance half times as did an oligonucleotide, which interacted with cell surface receptors. Manipulation of physiologic state (n=35) did not affect efflux, but sucrose efflux half time was longer with pentobarbital anesthesia (24 h) than with no anesthesia or ketamine-xylazine anesthesia (2 to 3 h). These results show that solute clearance from normal brain ECS may involve multiple physiologic pathways, may be affected by anesthesia, and suggests that convection-mediated efflux may be manipulated to increase or decrease drug clearance from brain.

Final report of the safety assessment of Urea

Although Urea is officially described as a buffering agent, humectant, and skin-conditioning agent-humectant for use in cosmetic products, there is a report stating that Urea also is used in cosmetics for its desquamating and antimicrobial action. In 2001, the Food and Drug Administration (FDA) reported that Urea was used in 239 formulations. Concentrations of use for Urea ranged from 0.01% to 10%. Urea is generally recognized as safe by FDA for the following uses: side-seam cements for food contact; an inhibitor or stabilizer in pesticide formulations and formulations applied to animals; internal sizing for paper and paperboard and surface sizing and coating of paper and paper board that contact water-in-oil dairy emulsions, low-moisture fats and oils, moist bakery products, dry solids with surface containing no free fats or oil, and dry solids with the surface of fat or oil; and to facilitate fermentation of wine. Urea is the end product of mammalian protein metabolism and the chief nitrogenous compound of urine. Urea concentrations in muscle, liver, and fetuses of rats increased after a subcutaneous injection of Urea. Urea diffused readily through the placenta and into other maternal and fetal organs. The half-life of Urea injected into rabbits was on the order of several hours, and the reutilization rate was 32.2% to 88.8%. Urea given to rats by a bolus injection or continuous infusion resulted in distribution to the following brain regions: frontal lobe, caudate nucleus, hippocampus, thalamus plus hypothalamus, pons and white matter (corpus callosum). The permeability constant after treatment with Urea of whole skin and the dermis of rabbits was 2.37 +/- 0.13 (x 10(6)) and 1.20 +/- 0.09 (x10(3)) cm/min, respectively. The absorption of Urea across normal and abraded human skin was 9.5% +/- 2.3% and 67.9% +/- 5.6%, respectively. Urea increased the skin penetration of other compounds, including hydrocortisone. No toxicity was observed for Urea at levels as high as 2000 mg/kg in acute oral studies using female rats or mice. No signs of toxicity were observed in male piglets dosed orally with up to 4 g/kg Urea for 5 days. Dogs dosed orally with 5 to 30 g/L Urea for 4 to 10 days had signs of toxicity, including weakness, anorexia, vomiting and retching, diarrhea and a decreased body temperature, which led to a deep torpor or coma. No significant microscopic changes were observed in the skin of male nude mice dermally exposed to 100% Urea for 24 h. No observable effect on fetal development was seen in rats and mice dosed orally with an aqueous solution of Urea (2000 mg/kg) on days 10 and 12 of gestation. The mean number of implants, live fetuses, percent fetal resorptions, mean fetal weight, and percent fetuses malformed were comparable to control group. A detergent containing 15% Urea was injected into pregnant ICR-JCl mice and dams and fetuses had no significant differences when compared to control animals. Urea given orally did not enhance the developmental toxicity of N-nitrosomethylurea. Female Sprague-Dawley rats injected in the uterine horn with 0.05 ml Urea on day 3 (preimplantation) or on day 7 (post implantation) exhibited no maternal mortality or morbidity; a dose-dependent reduction in embryo survival was seen with preimplantation treatment. Urea injected intra-amniotically induces mid-trimester abortions in humans. Urea was not genotoxic in several bacterial and mammalian assays; although in assays where Urea was used at a high concentration, genotoxicity was found, many in in vitro assays. Urea is commonly used in studies of DNA because it causes uncoiling of DNA molecules. Urea was not carcinogenic in Fisher 344 rats or C57B1/6 mice fed diets containing up to 4.5% Urea. Exposure of normal human skin to 60% Urea produced no significant irritation in one study, but 5% Urea was slightly irritating and 20% Urea was irritating in other reports. Burning sensations are the most frequently reported effect of Urea used alone or with other agents in treatment of diseased skin. Overall, there are few reports of sensitization among the many clinical studies that report use of Urea in treatment of diseased skin. The Cosmetic Ingredient Review (CIR) Expert Panel determined the data provided in this report to be sufficient to assess the safety of Urea. The Panel did note that Urea can cause uncoiling of DNA, a property used in many DNA studies, but concluded that this in vitro activity is not linked to any in vivo genotoxic activity. Although noting that formulators should be aware that Urea can increase the percutaneous absorption of other chemicals, the CIR Expert Panel concluded that Urea is safe as used in cosmetic products.

Use of a physiologically based pharmacokinetic model to study the time to reach brain equilibrium: an experimental analysis of the role of blood-brain barrier permeability, plasma protein binding, and brain tissue binding

This study was designed 1) to examine the effects of blood-brain barrier (BBB) permeability [quantified as permeability-surface area product (PS)], unbound fraction in plasma (f(u,plasma)), and brain tissue (f(u,brain)) on the time to reach equilibrium between brain and plasma and 2) to investigate the drug discovery strategies to design and select compounds that can rapidly penetrate the BBB and distribute to the site of action. The pharmacokinetics of seven model compounds: caffeine, CP-141938 [methoxy-3-[(2-phenyl-piperadinyl-3-amino)-methyl]-phenyl-N-methyl-methane-sulfonamide], fluoxetine, NFPS [N[3-(4'-fluorophenyl)-3-(4'-phenylphenoxy)propyl]sarcosine], propranolol, theobromine, and theophylline in rat brain and plasma after subcutaneous administration were studied. The in vivo log PS and log f(u,brain) calculated using a physiologically based pharmacokinetic model correlates with in situ log PS (R(2) = 0.83) and in vitro log f(u,brain) (R(2) = 0.69), where the in situ PS and in vitro f(u,brain) was determined using in situ brain perfusion and equilibrium dialysis using brain homogenate, respectively. The time to achieve brain equilibrium can be quantitated with a proposed parameter, intrinsic brain equilibrium half-life [t(1/2eq,in) = V(b)ln2/(PS . f(u,brain))], where V(b) is the physiological volume of brain. The in vivo log t(1/2eq,in) does not correlate with in situ log PS (R(2) < 0.01) but correlates inversely with log(PS . f(u,brain)) (R(2) = 0.85). The present study demonstrates that rapid brain equilibration requires a combination of high BBB permeability and low brain tissue binding. A high BBB permeability alone cannot guarantee a rapid equilibration. The strategy to select compounds with rapid brain equilibration in drug discovery should identify compounds with high BBB permeability and low nonspecific binding in brain tissue.

Airway eosinophils from actively sensitized guinea pigs exhibit enhanced superoxide anion release in response to antigen challenge

Antigen challenge of actively sensitized guinea pigs produces airway eosinophilia, airway hyperreactivity, and late-phase bronchoconstriction. The recruited eosinophils are thought to be important cells in the development of the airway hyperreactivity and the late-phase bronchoconstriction. However, the functional abilities of these eosinophils have not been determined in response to antigen challenge. The purpose of this study was to describe the characteristics of superoxide anion release from airway eosinophils obtained 24 h after ovalbumin challenge of actively sensitized guinea pigs. Eosinophils were collected by bronchoalveolar lavage. The total bronchoalveolar lavage eosinophil count was 17- to 27-fold greater in sensitized, ovalbumin-challenged guinea pigs (9.30 +/- 0.11 x 10(6)/guinea pig) than in unsensitized guinea pigs (0.35 +/- 0.07 x 10(6)/guinea pig) or sensitized, saline-challenged guinea pigs (0.56 x 10(6)/guinea pig; n = 2). The increase in eosinophils was due to increased lavage leukocyte count and increased eosinophil differential. Eosinophils were isolated on a Percoll-plasma discontinuous gradient. Two populations of eosinophils were collected, one at the 1.093 g/ml gradient step and one at the 1.107 g/ml gradient step. Unstimulated or phorbol myristate acetate (PMA)-stimulated superoxide anion release was measured by the reduction of ferricytochrome c. Unstimulated superoxide anion release from both eosinophil populations of challenged guinea pigs (4.50 +/- 2.37 and 4.07 +/- 1.48 nmol from 1.093 and 1.107 g/ml eosinophils, respectively) was 6- to 7-fold greater than superoxide anion release from eosinophils of control guinea pigs (0.74 +/- 0.43 and 0.56 +/- 025 nmol from 1.093 and 1.107 g/ml eosinophils, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Biophysical aspects of microsphere engulfment by human neutrophils

A quantitative investigation into the mechanism of neutrophil phagocytosis of opsonized microspheres possessing well defined dimensions was undertaken. Three aspects were documented: membrane conservation, cell adhesion to the spheres, and active cell cytoplasmic projection around the microspheres. The physical act of internalizing a particle by a cell involves a reduction in its plasma membrane area and an increase in its volume. As a consequence, a cell can internalize only a finite number of particles. A store of membrane area exists on cytoplasmic granules and may be recruited during phagocytosis. Previous measurements of neutrophil membrane area and volume served as a basis for estimates of the maximum number of internalized microspheres. A comparison with experimental prediction based on membrane conservation and degranulation agrees within 10% for a range of microsphere diameters, from 0.5 to 8 microns. This suggests that the limitation for additional particle uptake in the population of engorged neutrophils is the lack of excess plasma membrane area. In a random population of neutrophils, there was a sub-group, approximately 40%, which could no longer phagocytose before depleting their membrane stores. Several aspects of the engulfment process were investigated to elucidate the cause of this phagocytosis deficiency. It could be shown by single cell observation that these cases were associated with a lack of pseudopod projection, although adhesion was still evident between the cell membrane and the microspheres.

An in vivo kinetic model with L-[35S]methionine for the determination of local cerebral rates for methionine incorporation into protein in the rat

A method has been developed for the simultaneous in vivo measurement of local rates for methionine incorporation into cerebral protein in the rat. It is based on the use of L-[35S]methionine as a tracer for reflecting the bidirectional exchange of methionine between plasma and brain and its incorporation into cerebral protein, using a dynamic three-compartment model. An operational equation based on this model has been derived in terms of determinable variables. The method has been applied to the normal freely moving rat and to the rat under chloral hydrate anesthesia. In the freely moving rat, the values of methionine incorporation into cerebral protein in the gray matter vary widely from structure to structure (50-300 nmol/100 g/min), with the highest values in structures related to neurosecretory functions, e.g., supraoptic and paraventricular nuclei. The values for white matter are more uniform (24-28 nmol/100 g/min) at levels approximately six- to seven-fold lower than for gray matter. Chloral hydrate anesthesia depresses the rate of methionine incorporation in all the structures examined. Anesthesia did not reduce the heterogeneity normally present within gray matter.

Reduced pinosome formation in a cell-fusion-impaired mutant of mouse lymphocytic cell line L5178Y

Accumulation and release of a fluid-phase marker ([14C]-sucrose) were studied in a subline of the mouse lymphocytic cell line L5178Y and in a polyethylene glycol-resistant, intercellular-fusion-impaired mutant of this line. The mutant was found to accumulate [14C]-sucrose at a significantly slower rate than the parent. Analysis of release of preloaded label shows that the reduced rate of accumulation is due to a correspondingly low level of internalization, i.e., pinosome formation, rather than to a reduction in delivery of label to lysosomes. Cell-to-cell fusion and pinosome formation both involve a fusion event initiated at the extracellular surface of the plasma membrane, and we propose that the coordinate reduction in both processes suggests that they are mechanistically related.

Kinetic analysis of cerebrovascular isoleucine transport from saline and plasma

The concentration dependence of regional isoleucine transport across the blood-brain barrier was determined in anesthetized rats with the in situ brain perfusion technique of Takasato et al. [Am. J. Physiol. 247, H484-493 (1984)]. This technique allows, for the first time, accurate measurements of cerebrovascular amino acid transport in the absence of competing amino acids using saline perfusate, and in the presence of physiological concentrations of amino acids using plasma perfusate. Cerebrovascular isoleucine transport from saline perfusate followed Michaelis-Menten saturation kinetics where Vmax = 9 - 11 X 10(-4) mumol X s-1 X g-1 and Km = 0.054-0.068 mumol X ml-1 in six brain regions. A component of nonsaturable transport was not detected in any brain region even though perfusate isoleucine concentration was increased to greater than or equal to 150 times the normal plasma concentration. Isoleucine influx during plasma perfusion was only 8% of that predicted from the saline perfusion data due to transport inhibition by competing amino acids in plasma. Competitive inhibition increased the apparent Km for isoleucine transport from plasma by greater than or equal to 24-fold to 1.5-1.7 mumol X ml-1. These data provide accurate new estimates of the kinetic constants that describe amino acid transport across the blood-brain barrier. In addition, they indicate that the cerebrovascular transfer-site affinity (1/Km) for isoleucine is approximately fivefold greater than previously reported with the brain uptake index technique.

Phagocytic uptake of latex beads by rat peritoneal macrophages: comparison of morphological and radiochemical assay methods

Contrary to previous reports, commercially available 1000-nm latex beads were found to be labelable with 125I, yielding a product that retained its radiolabel on storage at 4 degrees C and when incubated in tissue-culture media. This finding permitted a radiochemical method to measure phagocytic uptake of latex particles by rat peritoneal macrophages cultured in vitro, and a direct comparison with the established method of particle counting by light microscopy. The two methods yielded closely similar data, demonstrating that the (much more convenient) radiochemical method for quantitating phagocytic uptake is both feasible and reliable. The kinetics of phagocytic uptake of the latex particles and the effect of low temperature and metabolic inhibitors (sodium fluoride and 2,4-dinitrophenol) are described. Ongoing phagocytosis did not alter the rate of fluid-phase pinocytosis by macrophages.

Carrier-mediated transport of chloride across the blood-brain barrier

36Cl concentrations in each of eight brain regions and in cisternal cerebrospinal fluid (CSF) were determined 30 min after the intravenous injection of 36Cl in dialyzed-nephrectomized rats with plasma Cl concentrations between 14 and 120 mumol X ml-1. CSF 36Cl exceeded 36Cl concentrations in brain extracellular fluid. The calculated blood-to-brain transfer constants for Cl, kCl, ranged from 1.8 X 10(-5) S-1 at the parietal cortex to 3.8 X 10(-5) S-1 at the thalamus-hypothalamus. kCl fell by 42-62% when mean plasma [Cl] was elevated from 16 to 114 mumol X ml-1. Brain uptake of [14C]mannitol or of 22Na was independent of plasma [Cl], but 22Na influx into CSF fell when plasma [Cl] was reduced. Cl flux into brain and CSF could be represented by Michaelis-Menten saturation kinetics, where, for the parietal cortex, Km = 43 mumol X ml-1 and Vmax = 2.5 X 10(-3) mumol X S-1 X g-1, and for CSF Km = 68 mumol X ml-1. At least 80% of 36Cl influx into the parietal cortex was calculated to occur at the cerebrovascular endothelium, whereas the remainder was derived from tracer that first entered CSF. The CSF contribution was greater at brain regions adjacent to cerebral ventricles. The results show that Cl transport at the cerebrovascular endothelium as well as at the choroid plexus epithelium is a saturable concentration-dependent process, and that the CSF is a significant intermediate pathway for Cl passage from blood to brain.

Pinocytosis and intracellular degradation of exogenous protein: modulation by amino acids

Intracellular degradation of exogenous (serum) proteins provides a source of amino acids for cellular protein synthesis. Pinocytosis serves as the mechanism for delivering exogenous protein to the lysosomes, the major site of intracellular degradation of exogenous protein. To determine whether the availability of extracellular free amino acids altered pinocytic function, we incubated monolayers of pulmonary alveolar macrophages with the fluid-phase marker, [14C]sucrose, and we dissected the pinocytic process by kinetic analysis. Additionally, intracellular degradation of endogenous and exogenous protein was monitored by measuring phenylalanine released from the cell monolayers in the presence of cycloheximide. Results revealed that in response to a subphysiological level of essential amino acids or to amino acid deprivation, (a) the rate of fluid-phase pinocytosis increased in such a manner as to preferentially increase both delivery to and size of an intracellular compartment believed to be the lysosomes, (b) the degradation of exogenously supplied albumin increased, and (c) the fraction of phenylalanine derived from degradation of exogenous albumin and reutilized for de novo protein synthesis increased. Thus, modulation of the pinosome-lysosome pathway may represent a homeostatic mechanism sensitive to the availability of extracellular free amino acids.