Passive Passage Research Articles

Overcoming Barriers Associated with Oral Delivery of Differently Sized Fluorescent Core-Shell Silica Nanoparticles.

Oral delivery, while a highly desirable form of nanoparticle-drug administration, is limited by challenges associated with overcoming several biological barriers. Here, the authors study how fluorescent and poly(ethylene glycol)-coated (PEGylated) core-shell silica nanoparticles sized 5 to 50nm interact with major barriers including intestinal mucus, intestinal epithelium, and stomach acid. From imaging fluorescence correlation spectroscopy studies using quasi-total internal reflection fluorescence microscopy, diffusion of nanoparticles through highly scattering mucus is progressively hindered above a critical hydrodynamic size around 20nm. By studying Caco-2 cell monolayers mimicking the intestinal epithelia, it is observed that ultrasmall nanoparticles below 10nm diameter (Cornell prime dots, [C' dots]) show permeabilities correlated with high absorption in humans from primarily enhanced passive passage through tight junctions. Particles above 20nm diameter exclusively show active transport through cells. After establishing C' dot stability in artificial gastric juice, in vivo oral gavage experiments in mice demonstrate successful passage through the body followed by renal clearance without protein corona formation. Results suggest C' dots as viable candidates for oral administration to patients with a proven pathway towards clinical translation and may generate renewed interest in examining silica as a food additive and its effects on nutrition and health.

Evidence of passive faecal shedding of Mycobacterium avium subsp. paratuberculosis in a Limousin cattle herd

It has been suggested that passive shedding of Mycobacterium avium subsp. paratuberculosis (MAP) in faeces may occur, but reliable data are missing. Passive shedding assumes the ingestion of MAP in contaminated feed and passive passage through the gastrointestinal tract without causing infection. In this study the presence of MAP in faeces in a closed herd of Limousin cattle was monitored for 53 months using quantitative real time PCR (qPCR) and culture. The initial prevalence of MAP in the herd was determined to be 63.4% and 4.9% using qPCR and culture, respectively. After the removal of two culture- and qPCR-positive (>104 MAP cells/g) cows, the prevalence of MAP using qPCR decreased to 42.1% and later to 15.6% and 6.7%. The continuous removal of suspected animals from the herd during the monitoring period minimised the presence of MAP in faeces to sporadic, which may have resulted from a decrease in the environmental infectious pressure. The findings suggest that the presence of low numbers of MAP in bovine faeces may not necessarily be caused by real infection, but rather by passive passage of MAP. This phenomenon should therefore be considered when interpreting MAP qPCR data.

Different Permeability of Potassium Salts across the Blood-Brain Barrier Follows the Hofmeister Series

The passage of ions across biological membranes is regulated by passive and active mechanisms. Passive ion diffusion into organs depends on the ion-pairing properties of salts present in the serum. Potassium ions could affect brain activity by crossing the blood-brain barrier (BBB) and its accumulation in the extracellular cerebral space could precipitate seizures. In the present study, we analyze passive diffusion of a series of potassium salts in the in vitro isolated guinea pig brain preparation. Different potassium counter-anions confer ion-pairing and lipophilicity properties that modulate membrane diffusion of the salt. Extracellular recordings in different cortical areas demonstrated the presence of epileptiform activities that strongly relate to anion identity, following the qualitative order of the Hofmeister series. Indeed, highly lipophilic salts that easily cross the BBB enhanced extracellular potassium concentration measured by ion-selective electrodes and were the most effective pro-epileptic species. This study constitutes a novel contribution for the understanding of the potential epileptogenicity of potassium salts and, more generally, of the role of counter-anions in the passive passage of salts through biological membranes.

Retrospective Study of the Risk Factors and Prevalence of Regurgitation in Dogs Undergoing General Anaesthesia

The records of 5736 general anaesthetics were reviewed to estimate the prevalence of, and identify the risk factors for, the development of regurgitation during anaesthesia in dogs. Regurgitation was defined as the observed passive passage of gastric contents into the oropharynx. Several variables were evaluated using univariable and multivariable logistic regression analysis: breed, body mass, age, sex, type of procedure, expertise of anaesthetist, ASA status, drugs administered, length of surgery and anaesthesia and local techniques performed. Results showed that larger dogs, dogs with ASA status of 3 or higher, dogs undergoing abdominal surgery, imaging procedures or both, longer anaesthetic duration, and dogs receiving medetomidine in comparison to acepromazine and an opioid were more likely to suffer an episode of regurgitation.

The multi‐faceted role of allergen exposure to the local airway mucosa

Airway epithelial cells are the first to encounter aeroallergens and therefore have recently become an interesting target of many studies investigating their involvement in the modulation of allergic inflammatory responses. Disruption of a passive structural barrier composed of epithelial cells by intrinsic proteolytic activity of allergens may facilitate allergen penetration into local tissues and additionally affect chronic and ongoing inflammatory processes in respiratory tissues. Furthermore, the ability of rhinoviruses to disrupt and interfere with epithelial tight junctions may alter the barrier integrity and enable a passive passage of inhaled allergens through the airway epithelium. On the other hand, epithelial cells are no longer considered to act only as a physical barrier toward inhaled allergens, but also to actively contribute to airway inflammation by detecting and responding to environmental factors. Epithelial cells can produce mediators, which may affect the recruitment and activation of more specialized immune cells to the local tissue and also create a microenvironment in which these activated immune cells may function and propagate the inflammatory processes. This review presents the dual role of epithelium acting as a passive and active barrier when encountering an inhaled allergen and how this double role contributes to the start of local immune responses.

Systematic analysis of barrier-forming FG hydrogels from Xenopus nuclear pore complexes

Nuclear pore complexes (NPCs) control the traffic between cell nucleus and cytoplasm. While facilitating translocation of nuclear transport receptors (NTRs) and NTR·cargo complexes, they suppress passive passage of macromolecules ⩾30 kDa. Previously, we reconstituted the NPC barrier as hydrogels comprising S. cerevisiae FG domains. We now studied FG domains from 10 Xenopus nucleoporins and found that all of them form hydrogels. Related domains with low FG motif density also substantially contribute to the NPC's hydrogel mass. We characterized all these hydrogels and observed the strictest sieving effect for the Nup98-derived hydrogel. It fully blocks entry of GFP-sized inert objects, permits facilitated entry of the small NTR NTF2, but arrests importin β-type NTRs at its surface. O-GlcNAc modification of the Nup98 FG domain prevented this arrest and allowed also large NTR·cargo complexes to enter. Solid-state NMR spectroscopy revealed that the O-GlcNAc-modified Nup98 gel lacks amyloid-like β-structures that dominate the rigid regions in the S. cerevisiae Nsp1 FG hydrogel. This suggests that FG hydrogels can assemble through different structural principles and yet acquire the same NPC-like permeability.

Analysis of correlation between cerebrospinal fluid and plasma HIV-1 RNA levels in patients with neurological opportunistic diseases

The question of whether HIV-1 RNA in cerebrospinal fluid (CSF) is derived from viral replication in the central nervous system or simply reflects the transit of infected lymphocytes from the blood compartment has long been a matter of debate. Some studies found no correlation between CSF and plasma viral load, whereas others did. The lack of a correlation between the two compartments suggests that the presence of HIV-1 RNA is not simply due to the passive passage of the virus from blood to CSF but rather due to intrathecal replication. To evaluate the correlation between plasma and CSF HIV-1 RNA levels and to identify situations in which there is no correlation between the two compartments, seventy patients were prospectively studied. The association between CSF and plasma viral load was evaluated in the total population and in subgroups of patients with similar characteristics. A correlation between the CSF and plasma compartments was observed for patients undergoing highly active antiretroviral therapy (HAART), those with a CD4 T lymphocyte count lower than 200 cells/mm³, and those with increased CSF protein content. On the other hand, no correlation was observed for patients without adequate virological control, who had a CD4 count higher than 200 cells/mm³ and who did not use HAART. The correlation between the two compartments observed in some patients suggests that CSF HIV-1 RNA levels may reflect plasma levels in these subjects. In contrast, the lack of a correlation between the two compartments in patients who were not on HAART and who had normal CSF proteins and a poor virological control possibly indicates compartmentalization of the virus in CSF and, consequently, plasma-independent intrathecal viral replication.

Epicutaneous Immunotherapy Results in Rapid Allergen Uptake by Dendritic Cells through Intact Skin and Downregulates the Allergen-Specific Response in Sensitized Mice

Epicutaneous immunotherapy onto intact skin has proved to be an efficient and safe alternative treatment of allergy in an animal model with various allergens and in children for cow's milk allergy. The aim of this study was to analyze the different steps of the immunological handling of the allergen when deposited on intact skin using an epicutaneous delivery system and its immune consequences in sensitized BALB/c mice. As expected, when applied on intact skin, OVA exhibits neither a passive passage through the skin nor any detectable systemic delivery. The current study demonstrates that, after a prolonged application on intact skin, OVA is taken up by dendritic cells in the superficial layers of the stratum corneum and transported, after internalization, to the draining lymph nodes, with variations according to the previous level of sensitization of the mice. When OVA is applied with the epicutaneous delivery system repeatedly, specific local and systemic responses are down-modulated in association with the induction of regulatory T cells. Besides providing new insights into skin function in the presence of allergens, this study indicates that the skin might have a tolerogenic role, at least when kept intact.

Characterisation of the passive permeability barrier of nuclear pore complexes

Nuclear pore complexes (NPCs) restrict uncontrolled nucleocytoplasmic fluxes of inert macromolecules but permit facilitated translocation of nuclear transport receptors and their cargo complexes. We probed the passive barrier of NPCs and observed sieve-like properties with a dominating mesh or channel radius of 2.6 nm, which is narrower than proposed earlier. A small fraction of diffusion channels has a wider opening, explaining the very slow passage of larger molecules. The observed dominant passive diameter approximates the distance of adjacent hydrophobic clusters of FG repeats, supporting the model that the barrier is made of FG repeat domains cross-linked with a spacing of an FG repeat unit length. Wheat germ agglutinin and the dominant-negative importin β45-462 fragment were previously regarded as selective inhibitors of facilitated NPC passage. We now observed that they do not distinguish between the passive and the facilitated mode. Instead, their inhibitory effect correlates with the size of the NPC-passing molecule. They have little effect on small species, inhibit the passage of green fluorescent protein-sized objects >10-fold and virtually block the translocation of larger ones. This suggests that passive and facilitated NPC passage proceed through one and the same permeability barrier.

Hepatitis C virus in the semen of men coinfected with HIV-1: prevalence and origin

To compare the prevalence of hepatitis C (HCV) RNA in semen from men infected with HCV and those coinfected with HIV-1/HCV and to study the origin of HCV shed in semen. Two prospective studies (HC EP09 and BINECO) included 120 HCV-positive men, 82 coinfected with HIV-1; all had positive HCV RNA detection in blood. Paired blood and semen samples were collected for HCV RNA detection and quantification in seminal plasma and in blood serum; repeated semen samples were obtained for 45 men. HCV RNA was sought in spermatozoa and non-sperm cells. Phylogenetic analysis of the HVR-1 region of HCV compared the quasispecies in blood serum and seminal plasma of two men. HCV RNA was more frequently found in the semen of men coinfected with HIV-1 (37.8%) than in those with only HCV infection (18.4%) (P = 0.033). HCV RNA detection in semen was intermittent and was positive in at least one semen sample of 42.8% of HIV-1/HCV-coinfected men who provided repeated samples. Men with HCV-positive semen had significantly higher HCV load in blood than men with HCV-negative semen (P = 0.038). Phylogenetic comparison of HCV quasispecies in blood and in semen showed no evidence of HCV replication in genital leukocytes; however, a phenetic structure was observed between compartments (P < 0.001). HCV particles in semen originate from passive passage from blood, with preferential transfer of some variants. Nearly half of HIV-1/HCV-coinfected men may intermittently harbour HCV in their semen. Recommendations of protected sex for HIV-infected individuals should be reinforced.

Pond production characteristics of freshwater prawns Macrobrachium rosenbergii as influenced by the stocking of size-graded populations of juveniles

A nursery-reared population of 50-day-old post-larvae of freshwater shrimp ( Macrobrachium rosenbergii) averaging 0.16 ± 0.08 g was divided into three groups. Two groups were size-graded by passive passage through either a 0.64 or a 0.48 cm mesh. Prawns passing through the 0.64 cm mesh proportionately graded into two size groups, 30% upper (0.40 ± 0.13 g) and 70% lower (0.15 ± 0.06 g). Size groups resulting from the 0.48 cm mesh grading were 70% upper (0.21 ± 0.09 g) and 30% lower (0.10 ± 0.03 g). Earthen ponds (0.061–0.073 ha) were stocked at a density of 39530/ha in triplicate with individuals from one of each of the graded or ungraded groups. After a 125- to 138-day growing season, average harvest weight ranged from 24.3 g (ungraded) to 35.4 g (30% upper) and differed significantly among treatments. Growth rates were not significantly different. Samples of prawns removed from each pond were classified into 5 morphotypes: blue claw male (BC), orange claw male + no clawed male (OCNC), small male (SM), berried female + open female (BFOF), and virgin female (VF). Mean harvest weights of the BFOF and OCNC categories in the 30% upper treatment were significantly greater than those for all other treatments. Average yield for the 30% upper and 70% upper treatments (1106 and 884 kg·ha −1, respectively) were significantly greater than that of the ungraded treatment (775 kg·ha −1). Differences in average harvest weight and total yield were achieved through changes in morphotype distributions. Calculated gross revenues in graded populations were 6–73% greater than that of the ungraded population.

Vanadyl (IV) and vanadate (V) binding to selected endogenous phosphate, carboxyl, and amino ligands; calculations of cellular vanadium species distribution

Vanadium enters cells as vanadate (V) where it is reduced to vanadyl (IV), VO 2+. Vanadate species at plasma pH, H 2VO 4 −, and HVO 4 2− are referred to as VO 3 −. To gain an insight into the subcellular vanadium distribution we measured the binding of VO 3 − and VO 2+ to extra- and intracellular ligands, and calculated free and bound fractions of these ions for expected in vivo conditions. The association constants ( K) were determined by the pH shift caused by an addition of VOSO 4 or NaVO 3 to individual ligand solutions at 20 °C and a pH equal to the p K of the reactive groups. The p k's for binding of VO 2+ were ATP, 5.9; ADP, 5.5; AMP, 5.1; P i 4.3; creatine phosphate (CP), 3.6; glutamic acid, 3.4; aspartic acid, 3.1; human serum albumin, 3.1; glutathione, 2.7; ascorbic acid, 3.3; citric acid, 4.0. The p k of VO 3 − and human serum albumin was 3.3 and of that VO 3 − and glutathione was 4.2. VO 3 − did not bind to ATP, even via Mg 2+ or Ca 2+ bridges. We calculated that in cells ~1% of total VO 2+ is unbound, which is 10 −10–10 −9 m since published values for total vanadium (mainly VO 2+) concentrations in tissues are on the order of 10 −8–10 −7 m. Free VO 2+ may be even less because of binding to additional ligands not considered and due to spontaneous hydrolysis to VOOH + and VO(OH) 2 2+ at intracellular pH. The binding of VO 2+ to each ligand was corrected for presence of multiple ligands and competition by H +, K +, and Mg 2+. In cells with no CP, up to 70% of VO 2+ is bound to phosphates and up to 29% to proteins; in cells with 30 m m CP (as in muscle), ~95% is bound to phosphates (CP binds up to 61% of total VO 2+) and ~4% to proteins; in cells with 2 m m ascorbic acid (as in brain), the vitamin binds ~3% of total VO 2+. These binding values apply for the total VO 2+ concentration range of 10 −8–10 −5 m. The intracellular binding and a reducing environment protect the freshly reduced VO 2+ from oxidation to VO 3 − that would otherwise occur at neutral pH. This strong affinity of VO 2+ primarily for phosphates also explains the mechanism for the intracellular accumulation of vanadium which is a factor in previously observed transport of VO 3 − into cells. Given 90% protein binding, free plasma VO 3 − would be ~10 −9 m, since total vanadium (mainly VO 3 −) concentration in human plasma is ~10 −8 m. Passive passage against the electrochemical gradient, calculated by the Nernst equation, would result in 3 × 10 −11 m free VO 3 − inside the cell, a concentration ~100-fold lower than the published dissociation constant of VO 3 − and the high affinity site of the (Na + + K +)-ATPase molecule. Thus, given cytoplasmic site of action of vanadium and absence of an active transport, normal intracellular concentrations of free VO 3 − and VO 2+ appear to be too low for the regulation of the (Na ++ K +)-pump. ATP deficiency causes redistribution of VO 2+ to other ligands but insufficient free VO 2+ is liberated to affect known susceptible enzymes. On the other hand, overdosing with VO 3 − is known to result in reduced (Na + + K +)-ATPase activity and renal damage.

Is there a blood-brain barrier at the optic nerve head?

The retina and optic nerve have been demonstrated to possess a blood-brain barrier that prevents the passive passage of protein and certain dyes from the blood vessels into the extracellular space. Our observations suggest that an exception is present at the normal optic disc. Using horseradish peroxidase as a tracer for electron microscopy and the normal rhesus monkey as the experimental animal, we have demonstrated that in certain regions of the optic nerve head, horseradish peroxidase from the blood stream reaches the axons of the optic nerve through the border tissue of Elschnig from the adjacent choridal tissues. A barrier formed by a series of cell junctions between glial cells at the edge of the optic disc prevented spread of the tracer from the optic disc into the subretinal space.

Surface Changes of Arachnoid Granulations With Varying Pressure Gradients A Scanning Electron Microscope Study

Most current ultrastructural studies of the arachnoid villi and granulations in mammals have not taken into account the maintenance of constant pressure gradients during perfusion and fixation showing arachnoid villi and granulations partially or totally collapsed. Recent ultrastructural studies of monkey arachnoid villi fixed at different pressure gradients showed that the endothelial cells covering the villi were flatter and further apart with shorter cell-to-cell overlappings as the gradient was increased. The spaces between these endothelial cells appeared irregular and widened possibly increasing the passive passage of cerebrospinal fluid across the villi and granulations. It has been also shown that during physiologically occurring positional changes in living animals the normally existing pressure gradient remained almost Constant.

Cerebrospinal fluid thyroxine.

Total and dialyzable thyroxine in cerebrospinal fluid and in serum were measured in 33 euthyroid patients with various neurological disorders and in 2 hypo-and 2 hyperthyroid patients. Total and dialyzable thyroxine in cerebrospinal fluid were found to be influenced by the protein concentration in cerebrospinal fluid and by the thyroid parameters in serum. Mean values for free thyroxine in the whole material were found to be almost identical in serum and in cerebrospinal fluid, suggesting a free passive passage of thyroxine through the blood-cerebrospinal fluid barrier. The total binding capacity of thyroxine was found to be higher in cerebrospinal fluid than in serum samples diluted to the same protein concentration as in cerebrospinal fluid, probably due to a higher concentration of prealbumin in cerebrospinal fluid.

Variations in plasma thyroxine during labour and early puerperium.

ABSTRACT Repeated determinations of plasma T4, PBI, dialysable T4 and free T4 were undertaken on 31 mothers of full-term infants and ten mothers of premature infants in the perinatal period. The blood samples were obtained 2–7 hours before delivery, at delivery, 3–6 hours after delivery, 6–12 hours after delivery and on the 2nd, 3rd–4th and 5th–6th day after birth. Similar investigations were also undertaken on cord blood. A significant increase in the mean value for plasma T4 of approximately 25 % was found from before delivery to the time of delivery. This was followed by a rapid decrease, so that a return to values observed before delivery occurred on the 2nd day after delivery. Dial. T4 did not alter during the rapid variations in the plasma T4. Plasma T4 was found to be significantly increased in maternal blood at delivery as compared with cord blood but there was no significant difference in the mean values for free T4 in the cord blood and the maternal blood at delivery, suggesting a free passive passage of T4 via the placenta. The variations found have not been described previously and they provide a possible explanation for the disagreements between the results of previous investigators. The reason for the variations and their significance in assessing possible equilibrium between free T4 in the maternal blood and cord blood are discussed.

To Have Been or Not to Have Been

ABSTRACT To the Editor:— Your editorial writer suggests making to have been a has been. The haves and the have nots should agree on such passivity passing. This grammatic crusade deserves much accolade. While we're passing on passives, let's not be passe. Let's pass the passive passage into the past.