Development of epimedin A complex drugs for treating the osteoporosis

Osteoporosis is the most common disease involving bone degeneration. As the age of the population increases, the prevalence of the disease is expected to rise. However, current treatment methods do not provide a desirable solution for the restoration of the function of degenerated bones in patients with osteoporosis. This led to emergence of controlled delivery systems to increase drug bioavailability and efficacy specifically at the bone regeneration. In this study, an epimedin A (EA) complex drug system was prepared by solution blending method. In vitro cell-based experiments showed that the EA complex drug could significantly promote the differentiation and proliferation of osteoblasts and increase the alkaline phosphatase activity, calcium nodule formation, and the expression of osteogenesis-related genes and proteins. In vivo experiments further demonstrated that this novel drugs remarkably enhanced bone regeneration. These results suggest that EA may be used for the treatment of osteoporosis.

Extended Pharmacokinetic Model of the Intravitreal Injections of Macromolecules in Rabbits. Part 2: Parameter Estimation Based on Concentration Dynamics in the Vitreous, Retina, and Aqueous Humor

PURPOSE

To estimate the diffusion coefficients of an IgG antibody (150 kDa) and its antigen-binding fragment (Fab; 50 kDa) in the neural retina (Dret) and the combined retinal pigment epithelium-choroid (DRPE-cho) with a 3-dimensional (3D) ocular pharmacokinetic (PK) model of the rabbit eye.

METHODS

Vitreous, retina, and aqueous humor concentrations of IgG and Fab after intravitreal injection in rabbits were taken from Gadkar et al. (2015). A least-squares method was used to estimate Dret and DRPE-cho with the 3D finite element model where mass transport was defined with diffusion and convection. Different intraocular pressures (IOP), initial distribution volumes (Vinit), and neural retina/vitreous partition coefficients (Kret/vit) were tested. Sensitivity analysis was performed for the final model.

RESULTS

With the final IgG model (IOP 10.1 Torr, Vinit 400 μl, Kret/vit 0.5), the estimated Dret and DRPE-cho were 36.8 × 10-9 cm2s-1 and 4.11 × 10-9 cm2s-1, respectively, and 76% of the dose was eliminated via the anterior chamber. Modeling of Fab revealed that a physiological model parameter "aqueous humor formation rate" sets constraints that need to be considered in the parameter estimation.

CONCLUSIONS

This study extends the use of 3D ocular PK models for parameter estimation using simultaneously macromolecule concentrations in three ocular tissues.

Distribution and Diffusion of Macromolecule Delivery to the Brain via Focused Ultrasound using Magnetic Resonance and Multispectral Fluorescence Imaging

Focused ultrasound (FUS), in combination with microbubble contrast agents, can be used to transiently open the blood-brain barrier (BBB) to allow intravascular agents to cross into the brain. Often, FUS is carried out in conjunction with magnetic resonance imaging (MRI) to evaluate BBB opening to gadolinium-based MRI contrast agents. Although MRI allows direct visualization of the distribution of gadolinium-based contrast agents in the brain parenchyma, it does not allow measurements of the distribution of other molecules crossing the BBB. Therapeutic molecules (e.g., monoclonal antibodies) are much different in size than MRI contrast agents and have been found to have different distributions in the brain after FUS-mediated BBB opening. In the work described here, we combined in vivo MRI and ex vivo multispectral fluorescence imaging to compare the distributions of MRI contrast and dextran molecules of different molecular weights (3, 70 and 500 kDa) after FUS-mediated BBB opening through a range of ultrasound pressures (0.18-0.46 MPa) in laboratory mice. The volume of brain exposed was calculated from the MRI and fluorescence images and was significantly dependent on both molecular weight and ultrasound pressure. Diffusion coefficients of the different-molecular-weight dextran molecules in the brain parenchyma were also calculated from the fluorescence images and were negatively correlated with the molecular weight of the dextran molecules. The results of this work build on a body of knowledge that is critically important for the FUS technique to be used in clinical delivery of therapeutics to the brain.

Nanoparticle-Enabled Transdermal Drug Delivery Systems for Enhanced Dose Control and Tissue Targeting

Transdermal drug delivery systems have been around for decades, and current technologies (e.g., patches, ointments, and creams) enhance the skin permeation of low molecular weight, lipophilic drugs that are efficacious at low doses. The objective of current transdermal drug delivery research is to discover ways to enhance skin penetration of larger, hydrophilic drugs and macromolecules for disease treatment and vaccination. Nanocarriers made of lipids, metals, or polymers have been successfully used to increase penetration of drugs or vaccines, control drug release, and target drugs to specific areas of skin in vivo. While more research is needed to identify the safety of nanocarriers, this technology has the potential to expand the use of transdermal routes of administration to a wide array of therapeutics. Here, we review the current state of nanoparticle skin delivery systems with special emphasis on targeting skin diseases.

Microanalysis, Pharmacokinetics and Tissue Distribution of Polysaccharide-Protein Complexes from Longan Pulp in Mice

A high performance size exclusion-fluorescence detection (HPSEC-FD) method combined with fluorescein isothiocyanate (FITC) prelabeling was established for the microanalysis of polysaccharide-protein complexes from longan pulp (LPP). FITC-labeled LPP (LPPF) was fractionated by gel filtration chromatography. The weight-average molecular weight and FITC substitution degree of LPPF were 39.01 kDa and 0.20%, respectively. The HPSEC-FD calibration curves linear over the range of 1-200 µg/mL in mouse plasma, spleen and lung samples with correlation coefficients greater than 0.995. The inter-day and intra-day precisions of the method were not more than 6.9%, and the relative recovery ranged from 93.7% to 106.4%. The concentration-time curve of LPPF in plasma following intravenous (i.v.) administration at 40 mg/kg body weight well fitted to a two-compartment model. LPPF rapidly eliminated from plasma according to the short half-lives (t1/2α=2.23 min, t1/2β=39.11 min) and mean retention times (MRT0-t=1.15 h, MRT0-∞=1.39 h). After administration over 5 to 360 min, the concentration of LPPF in spleen homogenate decreased from 7.41 to 3.68 µg/mL; the concentration in lung homogenate decreased from 9.08 to 3.40 µg/mL. On the other hand, the increasing concentration of LPPF fraction with low molecular weight in heart homogenate was observed.

Synthesis and characterization of a library of in-situ curing, nonswelling ethoxylated polyol thiol-ene hydrogels for tailorable macromolecule delivery

A transesterfication reaction is used to synthesize tri-thiol-functionalized-ethoxylated polyols that are combined with polyethylene glycol diacrylates to form a biodegradable hydrogel library. Hydrogels display nonswelling equilibration and offer temporal control over material degradation and the release of biomolecules. The demonstrated in vitro biocompatibility makes this a versatile platform that can be used for local drug delivery to volume-constrained anatomical sites.

Elevated uptake of plasma macromolecules by regions of arterial wall predisposed to plaque instability in a mouse model

Atherosclerosis may be triggered by an elevated net transport of lipid-carrying macromolecules from plasma into the arterial wall. We hypothesised that whether lesions are of the thin-cap fibroatheroma (TCFA) type or are less fatty and more fibrous depends on the degree of elevation of transport, with greater uptake leading to the former. We further hypothesised that the degree of elevation can depend on haemodynamic wall shear stress characteristics and nitric oxide synthesis. Placing a tapered cuff around the carotid artery of apolipoprotein E -/- mice modifies patterns of shear stress and eNOS expression, and triggers lesion development at the upstream and downstream cuff margins; upstream but not downstream lesions resemble the TCFA. We measured wall uptake of a macromolecular tracer in the carotid artery of C57bl/6 mice after cuff placement. Uptake was elevated in the regions that develop lesions in hyperlipidaemic mice and was significantly more elevated where plaques of the TCFA type develop. Computational simulations and effects of reversing the cuff orientation indicated a role for solid as well as fluid mechanical stresses. Inhibiting NO synthesis abolished the difference in uptake between the upstream and downstream sites. The data support the hypothesis that excessively elevated wall uptake of plasma macromolecules initiates the development of the TCFA, suggest that such uptake can result from solid and fluid mechanical stresses, and are consistent with a role for NO synthesis. Modification of wall transport properties might form the basis of novel methods for reducing plaque rupture.

Potential pharmacokinetic interactions of therapeutic cytokines or cytokine modulators on small-molecule drugs: mechanistic understanding via studies using in vitro systems

The potential pharmacokinetic interactions between macromolecules and small-molecule drugs have received more and more attention with the increasing development of macromolecule therapeutics. Studies have shown that cytokines can differentially modulate drug-metabolizing enzymes and transporters, which raises concerns on the potential interactions of therapeutic cytokines and cytokine modulators on the disposition of small-molecule drugs. Although many in vitro studies have been conducted to characterize the effects of cytokines on drug-metabolizing enzymes and transporters, these studies were limited to only a handful of cytokines, such as interleukin-1 (IL-1), IL-6, tumor necrosis factor-α, and interferon. It is also challenging to translate these in vitro results to in vivo. In addition, information on the impact of cytokine modulators on drug-metabolizing enzymes and transporters is rather limited. More research is needed in this area. The present review is to provide a summary of the in vitro findings on the pharmacokinetic interactions of therapeutic cytokines and cytokine modulators on small-molecule drugs. Discussion on current challenges in assessing these interactions is also included.

Physiology of the intrathecal bolus: the leptomeningeal route for macromolecule and particle delivery to CNS

Presently, there are no effective treatments for several diseases involving the CNS, which is protected by the blood-brain, blood-CSF, and blood-arachnoid barriers. Traversing any of these barriers is difficult, especially for macromolecular drugs and particulates. However, there is significant experimental evidence that large molecules can be delivered to the CNS through the cerebrospinal fluid (CSF). The flux of the interstitial fluid in the CNS parenchyma, as well as the macro flux of CSF in the leptomeningeal space, are believed to be generally opposite to the desirable direction of CNS-targeted drug delivery. On the other hand, the available data suggest that the layer of pia mater lining the CNS surface is not continuous, and the continuity of the leptomeningeal space (LMS) with the perivascular spaces penetrating into the parenchyma provides an unexplored avenue for drug transport deep into the brain via CSF. The published data generally do not support the view that macromolecule transport from the LMS to CNS is hindered by the interstitial and CSF fluxes. The data strongly suggest that leptomeningeal transport depends on the location and volume of the administered bolus and consists of four processes: (i) pulsation-assisted convectional transport of the solutes with CSF, (ii) active "pumping" of CSF into the periarterial spaces, (iii) solute transport from the latter to and within the parenchyma, and (iv) neuronal uptake and axonal transport. The final outcome will depend on the drug molecule behavior in each of these processes, which have not been studied systematically. The data available to date suggest that many macromolecules and nanoparticles can be delivered to CNS in biologically significant amounts (>1% of the administered dose); mechanistic investigation of macromolecule and particle behavior in CSF may result in a significantly more efficient leptomeningeal drug delivery than previously thought.

Diffusion of macromolecules through sclera

PURPOSE

To quantify the in vitro permeability coefficient over different topographical locations of porcine sclera to macromolecules with different molecular weight.

METHODS

Fresh equatorial and posterior superotemporal porcine sclera was mounted in a two-chamber diffusion apparatus, and its permeability to fluorescein isothiocyanate (FITC)-conjugated dextrans ranging in molecular weight from 40 kDa to 150 kDa was determined by fluorescence spectrophotometry. The sclera was processed as frozen sections and viewed with a fluorescence microscope. The thickness of the area and the thickness that macromolecules enriched in the surface of sclera were measured.

RESULTS

The permeability coefficient (Pc) of porcine sclera to macromolecules was significantly higher (40 kDa, p = 0.028; 70 kDa, p = 0.033; 150 kDa, p = 0.007) in equatorial region than posterior, which could be attributed to the significant difference of thickness (p < 0.001, Kruskal-Wallis) between them. Moreover, linear regression indicated a significant negative relationship (40 kDa, p < 0.001; 70 kDa, p = 0.015; 150 kDa, p < 0.001) between scleral permeability coefficient and thickness. Also, Pc declined significantly with increasing molecular weight (MW, p < 0.001, Kruskal-Wallis). The area that the macromolecules enriched in the scleral surface was thicker for those with larger MW (p < 0.001, Kruskal-Wallis). The maximum MW and size for equatorial and posterior superotemporal scleral tissue were 185.01 KDa and 180.42 KDa, 9.92 nm and 9.67 nm, respectively.

CONCLUSIONS

The permeability coefficient of porcine sclera has a significant negative relationship with scleral thickness and MW of macromolecules. Larger macromolecules are more likely to accumulate in scleral surface. The difference between topographical locations may have pharmacokinetic implications when considering transscleral diffusion of macromolecules.

Vascular permeability in cancer and infection as related to macromolecular drug delivery, with emphasis on the EPR effect for tumor-selective drug targeting

Tumor and inflammation have many common features. One hallmark of both is enhanced vascular permeability, which is mediated by various factors including bradykinin, nitric oxide (NO), peroxynitrite, prostaglandins etc. A unique characteristic of tumors, however, is defective vascular anatomy. The enhanced vascular permeability in tumors is also distinctive in that extravasated macromolecules are not readily cleared. We utilized the enhanced permeability and retention (EPR) effect of tumors for tumor selective delivery of macromolecular drugs. Consequently, such drugs, nanoparticles or lipid particles, when injected intravenously, selectively accumulate in tumor tissues and remain there for long periods. The EPR effect of tumor tissue is frequently inhomogeneous and the heterogeneity of the EPR effect may reduce the tumor delivery of macromolecular drugs. Therefore, we developed methods to augment the EPR effect without inducing adverse effects for instance raising the systemic blood pressure by infusing angiotensin II during arterial injection of SMANCS/Lipiodol. This method was validated in clinical setting. Further, benefits of utilization of NO-releasing agent such as nitroglycerin or angiotensin-converting enzyme (ACE) inhibitors were demonstrated. The EPR effect is thus now widely accepted as the most basic mechanism for tumor-selective targeting of macromolecular drugs, or so-called nanomedicine.

[M cell in vitro model and its application in oral delivery of macromolecular drugs]

The oral administration of bioactive macromolecular drugs such as proteins, peptides and nucleic acids represents unprecedented challenges from the drug delivery point of view. One key consideration is how to overcome the gastrointestinal tract absorption barrier. Recent studies suggest that microfold cell (M cell), a kind of specialized antigen-sampling epithelial cell which is characterized by a high endocytic rate and low degradation ability, may play an important role in macromolecule oral absorption. The development of an in vitro M cell coculture system and its modified models greatly advanced the study of M cells and the development of oral delivery system for macromolecular drugs. The special structure, function and formation characteristics, and biomarkers of M cell are summarized in this review. The applications of in vitro M cell models in developing oral delivery system ofbioactive macromolecular drugs are discussed.

Application of accelerator mass spectrometry to macromolecules: preclinical pharmacokinetic studies on a polybisphosphonate

Data on the use of accelerator mass spectrometry (AMS) in conjunction with in vivo studies of macromolecular drugs are scarce. The present study shows the versatility of this technique when investigating the pharmacokinetics (PK) of a macromolecular drug candidate, a polybisphosphonate conjugate (ODX). The aforementioned is a polymer (molecular weight ~30 kDa) constituting a carbohydrate backbone with covalently linked ligands (aldendronate and aminoguanidine) and is intended for treatment of osteoporosis and the therapy of bone metastasis from prostate cancer. The conjugate is prepared through partial oxidation of the carbohydrate and sequential coupling of the ligands by reductive amination. (14)C was incorporated in the conjugate by means of coupling a commercially available (14)C-lysine in the conjugation sequence. Fifteen rats were injected intravenously with (14)C-labelled ODX (150 µg, 14 Bq/rat) and blood samples were collected at 1, 2, 4, 6, and 24 h post-injection (3 rats/time point). Liver, spleen and kidney samples were collected at 4 and 24 h post-injection. Blood from each time point (triplicate) were collected for AMS measurement determining the isotopic ratio ((14)C/(12)C) and consequently the drug concentration in blood. ODX showed a transient presence in blood circulation; 93% of the total dose was cleared from the circulation within 1 h. The half-life after 1 h was estimated to be about 3 h; 0.7% of the administered (14)C dose of ODX remained in circulation after 24 h. The major (14)C accumulation was in the liver, the spleen and the kidneys indicating the probable route of metabolism and excretion. This study demonstrates the versatility of AMS for pharmacological in vivo studies of macromolecules. Labelling with (14)C is relatively simple, inexpensive and the method requires minimal radioactivity, eliminating the need for radioprotection precautions in contrast to methods using scintillation counting.

Ultrasound enhanced delivery of macromolecular agents in brain tumor rat model

The purpose of this study was to evaluate the permeability of the blood-brain barrier (BBB) after focused ultrasound (FUS) exposure and to investigate if such an approach increases the tumor-to-ipsilateral brain permeability ratio. Normal rats and F98 glioma-bearing rats were injected intravenously with Evans blue (EB); these treatments took place with or without BBB disruption induced by transcranial FUS of one hemisphere of the brain. Sonication was applied at an ultrasound frequency of 1 MHz with a 5% duty cycle, and a repetition frequency of 1 Hz. The permeability of the BBB was quantitatively assessed by means of the extravasation of EB. Contrast-enhanced MR images were used to monitor the gadolinium deposition path associated with transcranial FUS and the influence of size and location was also investigated. Furthermore, whole brain histological analysis was performed. The results were compared by two-tailed unpaired t test. The accumulation of EB in brains and the tumor-to-ipsilateral brain permeability ratio of EB were significantly increased after FUS exposure. EB injection followed by sonication showed an increase in the tumor-to-ipsilateral brain ratio of the target tumors of about two-fold compared with the control tumors on day 8 after tumor implantation. MR images showed that FUS locally enhances the permeability of the BBB in the glioma-bearing rats. The BBB can be locally disrupted with FUS in the presence of microbubbles. This technology may offer new opportunities that will allow enhanced synergistic effects with respect to other brain tumor treatment regimens.

Cavitation-enhanced delivery of macromolecules into an obstructed vessel

Poor drug penetration through tumor tissue has emerged as a fundamental obstacle to cancer therapy. The aim of this study was to examine the ability of cavitation instigated by high-intensity focused ultrasound (HIFU) to increase convective transport of a model therapeutic in an in vitro tumor model. Cavitation activity was quantified by analyzing passively recorded acoustic emissions, and mass transfer was quantified using post-treatment image analysis of the distribution of a dye-labeled macromolecule. The strong correlation between cavitation activity and drug delivery suggests the potential for non-invasive treatment and monitoring.

Acute and chronic exposure to shear stress have opposite effects on endothelial permeability to macromolecules

Endothelial properties are affected by mechanical stresses. Several studies have shown that an acute application of shear stress increases the permeability of endothelial monolayers in culture. We investigated whether more prolonged application of shear has the opposite effect. Porcine aortic endothelial cells were cultured on Transwell filters to assess monolayer permeability to albumin. The medium above the cells was swirled using an orbital shaker; resultant shears were computed to lie within the physiological range. Acute application of shear increased permeability, but chronic application reduced it. The effect of chronic but not acute shear was reversed by inhibiting nitric oxide (NO) synthesis. The effect of chronic shear was also reversed by inhibiting phosphatidylinositol 3-OH kinase (PI3K) and soluble guanylyl cyclase. None of these interventions affected permeability under static conditions, and inhibition of cyclooxygenase was without effect. Chronic shear decreased mitosis rates by a fraction comparable to the reduction in permeability, but this effect was not reversed by inhibiting NO synthesis. We conclude that chronic application of shear stress reduces endothelial permeability to macromolecules by a PI3K-NO-cGMP-dependent mechanism. Since atherosclerosis can be triggered by excessive entry of plasma macromolecules into the arterial wall, the phenomenon may help explain the atheroprotective effects of shear and NO.

Physiologically-based PK/PD modelling of therapeutic macromolecules

Therapeutic proteins are a diverse class of drugs consisting of naturally occurring or modified proteins, and due to their size and physico-chemical properties, they can pose challenges for the pharmacokinetic and pharmacodynamic studies. Physiologically-based pharmacokinetics (PBPK) modelling has been effective for early in silico prediction of pharmacokinetic properties of new drugs. The aim of the present workshop was to discuss the feasibility of PBPK modelling of macromolecules. The classical PBPK approach was discussed with a presentation of the successful example of PBPK modelling of cyclosporine A. PBPK model was performed with transport of the cyclosporine across cell membranes, affinity to plasma proteins and active membrane transporters included to describe drug transport between physiological compartments. For macromolecules, complex PBPK modelling or permeability-limited and/or target-mediated distribution was discussed. It was generally agreed that PBPK modelling was feasible and desirable. The role of the lymphatic system should be considered when absorption after extravascular administration is modelled. Target-mediated drug disposition was regarded as an important feature for generation of PK models. Complex PK-models may not be necessary when a limited number of organs are affected. More mechanistic PK/PD models will be relevant when adverse events/toxicity are included in the PK/PD modelling.

Mathematical modeling of molecular diffusion through mucus

The rate of molecular transport through the mucus gel can be an important determinant of efficacy for therapeutic agents delivered by oral, intranasal, intravaginal/rectal, and intraocular routes. Transport through mucus can be described by mathematical models based on principles of physical chemistry and known characteristics of the mucus gel, its constituents, and of the drug itself. In this paper, we review mathematical models of molecular diffusion in mucus, as well as the techniques commonly used to measure diffusion of solutes in the mucus gel, mucus gel mimics, and mucosal epithelia.

Macromolecular delivery across the blood-brain barrier

The delivery of macromolecules into the central nervous system (CNS) via the blood stream is seriously limited by the blood-brain barrier (BBB). Noninvasive, transient, and local image-guided blood-brain barrier disruption (BBBD) can be accomplished using focused ultrasound exposure with intravascular injection of pre-formed microbubbles. A detailed description of the method for MRI-guided focal BBBD in animals will be described in this chapter. The method may open a new era in CNS macromolecular drug delivery.

In vitro systems for studying epithelial transport of macromolecules

Biological barriers, typically, represented by epithelial tissues are the main hindrance against uncontrolled uptake of a variety of substances. However, the delivery across a biological barrier is a crucial factor in the development of drugs. As the permeability of macromolecular drugs is very limited, new delivery strategies have to be developed and further improved. Thereby, nanoparticle carriers offer an enormous potential for the controlled delivery of active substances into the organism. Besides an intensive study for the reason of risk assessment and toxicology, the possible transport enhancement caused by nanoparticles must be quantified. A powerful tool for these studies is in vitro cell culture models imitating the more complex in vivo situation under controlled conditions. We use polyethylenimine as model enhancer mimicking toxicological effects and altered barrier function in the epithelial in vitro model, Calu-3. Cytotoxicity assays based on different mechanisms and transport properties of a low-permeability marker with and without delivery enhancer are described.

Glycosilated Macromolecular Conjugates of Antiviral Drugs with a Polyaspartamide

Two new polymeric conjugates for specific liver targeting were prepared by conjugation of sugar moieties and antiviral drugs to alpha, beta-poly[N-2-(hydroxyethyl)-DL-aspartamide] (PHEA). PHEA-galactopyranosylphenylthiocarbamide-mono-O-succinylganciclovir (conjugate 7) and PHEA-mannopyranosylphenylthiocarbamide-O-succinylacyclovir (conjugate 8) were synthesized according to a multi-step procedure which allowed for obtaining high product yield and process standardization. Conjugate 7 contained 7.5 and 8.5% of galactose and ganciclovir (substituent/repeating unit, mol/mol), respectively, and conjugate 8 contained 14.2 and 10.8% of mannose and acyclovir, respectively. In vitro studies demonstrated that both acyclovir and ganciclovir are released from the polymeric adducts at a release rate, which depended on the incubation medium. Though a detailed study evidenced that the two bioconjugates undergo different hydrolysis pathways, in both cases high drug release rate was found in plasma, while the glycosidic moiety was not released. Pharmacokinetic studies carried out by intravenous administration of the bioconjugates to Balb/c mice demonstrated that the conjugation of glycosidic moieties promotes the disappearance of the polymer from the bloodstream. The two derivatives displayed a different pharmacokinetic profile. In particular, the mannosyl conjugation promoted the rapid disposition of the macromolecule in the kidneys and in the liver, while prevented the accumulation in the spleen. On the contrary, the galactosyl derivative was found to dispose in the liver at the same extent of the naked polymer. Few considerations on the different behavior of the conjugates were reported.

Structural effect on degradability and in vivo contrast enhancement of polydisulfide Gd(III) complexes as biodegradable macromolecular MRI contrast agents

The structural effect of biodegradable macromolecular magnetic resonance imaging (MRI) contrast agents, polydisulfide gadolinium (Gd)(III) chelates, on their in vitro degradability, and cardiovascular and tumor imaging were evaluated in mice. Polydisulfide Gd(III) chelates, Gd-DTPA cystamine copolymers (GDCC), Gd-DTPA l-cystine copolymers (GDCP), Gd-DTPA d-cystine copolymers (dGDCP) and Gd-DTPA glutathione (oxidized) copolymers (GDGP), with different sizes and narrow molecular weight distribution were prepared and evaluated both in vitro and in vivo in mice bearing MDA-MB-231 tumor xenografts. GDGP with large steric hindrance around the disulfide bonds had greater T(1) and T(2) relaxivities than GDCC, GDCP and dGDCP. The degradability of the polydisulfide by the endogenous thiols decreased with increasing steric effects around the disulfide bonds in the order of GDCC>GDCP, dGDCP>GDGP. The size and degradability of the contrast agents had a significant impact on vascular contrast enhancement kinetics. The agents with a large size and low degradability resulted in more prolonged vascular enhancement than the agents with a small size and high degradability. It seems that the size and degradability of the agents did not significantly affect tumor enhancement. All agents resulted in significant contrast enhancement in tumor tissue. This study has demonstrated that the vascular enhancement kinetics of the polydisulfide MRI contrast agents can be controlled by their sizes and structures. The polydisulfide Gd(III) chelates are promising biodegradable macromolecular MRI contrast agents for magnetic resonance angiography and cancer imaging.

The role of the lymphatic system in subcutaneous absorption of macromolecules in the rat model

The purpose of this study was to assess the contribution of lymphatics to the systemic bioavailability of macromolecules following SC administration in a rat model. The rat model included continuous lymph collection from the thoracic lymph duct and concurrent serial blood sampling from freely moving animals. A thoracic lymph duct-jugular vein shunt produced by an implanted connective cannula, and maintained during the recovery period, enabled superior rat survival and prevented lymphatic cannula occlusion. The SC absorption of three macromolecules (bovine insulin, bovine serum albumin, and recombinant human erythropoietin alpha) was assessed in comparison to the non-lymph cannulated control group. For all tested molecules, only minimal amounts (less than 3%) of the SC administered dose were detected in the collected lymph. In the rat model, following SC administration, the macromolecules were absorbed mainly through the blood capillaries with minimal contribution of the lymphatic system to systemic bioavailability. The relatively small elevation in the lymphatic concentration, which occurred in all molecules, may be attributed to the redistribution of the molecules from the blood to the interstitial fluid compartment. These findings are important since rodents are commonly used in preclinical evaluation of macromolecular drugs.

The HA proteins of botulinum toxin disrupt intestinal epithelial intercellular junctions to increase toxin absorption

The type B botulinum neurotoxin (BoNT) elicits flaccid paralysis and death in humans by intoxicating peripheral nerves after oral absorption. Here, we examine the function of the haemagglutinin (HA), a non-toxic component of the large 16S BoNT complex. We find that the HA acts in the intestine to disrupt epithelial barrier function by opening intercellular tight and adherens junctions. This allows transport of BoNT and other large solutes into the systemic circulation and explains how the type B BoNT complexes are efficiently absorbed. In vitro, HA appears to act on the epithelial cell via the basolateral membrane only, suggesting the possibility of another step in the absorptive process. These studies show that the 16S BoNT complex is a multifunctional protein assembly equipped with the machinery to efficiently breach the intestinal barrier and act systemically on peripheral nerves.

Key elements of bioanalytical method validation for macromolecules

The Third American Association of Pharmaceutical Scientists/US Food and Drug Administration (FDA) Bioanalytical Workshop, which was held May 1 and 2, 2006, in Arlington, VA, addressed bioanalytical assays that are being used for the quantification of therapeutic candidates in support of pharmacokinetic evaluations. One of the main goals of this workshop was to discuss best practices used in bioanalysis regardless of the size of the therapeutic candidates. Since the last bioanalytical workshop, technological advancements in the field and in the statistical understanding of the validation issues have generated a variety of interpretations to clarify and understand the practicality of using the current FDA guidance for assaying macromolecular therapeutics. This article addresses some of the key elements that are essential to the validation of macromolecular therapeutics using ligand binding assays. Because of the nature of ligand binding assays, attempts have been made within the scientific community to use statistical approaches to interpret the acceptance criteria that are aligned with the prestudy validation and in-study validation (sample analysis) processes. We discuss, among other topics, using the total error criterion or confidence interval approaches for acceptance of assays and using anchor calibrators to fit the nonlinear regression models.

Drug targeting to the brain

The central nervous system (CNS) is a sanctuary site and is protected by various barriers. These regulate brain homeostasis and the transport of endogenous and exogenous compounds by controlling their selective and specific uptake, efflux, and metabolism in the brain. Unfortunately, potential drugs for the treatment of most brain diseases are therefore often not able to cross these barriers. As a result, various drug delivery and targeting strategies are currently being developed to enhance the transport and distribution of drugs into the brain. Here we discuss briefly the biology and physiology of the blood-brain barrier (BBB) and the blood-cerebro-spinal-fluid barrier (BCSFB), and, in more detail, the possibilities for delivering large-molecular-weight drugs by local and global delivery and by viral and receptor-mediated nonviral drug delivery to the (human) brain.

Cellular uptake of cationic polymer-DNA complexes via caveolae plays a pivotal role in gene transfection in COS-7 cells

PURPOSE

Knowledge about the uptake mechanism and subsequent intracellular routing of non-viral gene delivery systems is important for the development of more efficient carriers. In this study we compared two established cationic polymers pDMAEMA and PEI with regard to their transfection efficiency and mechanism of cellular uptake.

MATERIALS AND METHODS

The effects of several inhibitors of particular cellular uptake routes on the uptake of polyplexes and subsequent gene expression in COS-7 cells were investigated using FACS and transfection. Moreover, cellular localization of fluorescently labeled polyplexes was assessed by spectral fluorescence microscopy.

RESULTS

Both pDMAEMA- and PEI-complexed DNA showed colocalization with fluorescently-labeled transferrin and cholera toxin after internalization by COS-7 cells, which indicates uptake via the clathrin- and caveolae-dependent pathways. Blocking either routes of uptake with specific inhibitors only resulted in a marginal decrease in polyplex uptake, which may suggest that uptake routes of polyplexes are interchangeable. Despite the marginal effect of inhibitors on polyplex internalization, blocking the caveolae-mediated uptake route resulted in an almost complete loss of polyplex-mediated gene expression, whereas gene expression was not negatively affected by blocking the clathrin-dependent route of uptake.

CONCLUSIONS

These results show the importance of caveolae-mediated uptake for successful gene expression and have implications for the rational design of non-viral gene delivery systems.

Intracellular delivery of oligonucleotide conjugates and dendrimer complexes

Enhancing the delivery of antisense and siRNA molecules to cells and tissues is a key issue for oligonucleotide therapeutics. Cell-penetrating peptides (CPPs) have the ability to convey linked "cargo" molecules into the cytosol; thus we have explored the use of CPPs as delivery agents for oligonucleotides. We have extensively evaluated CPP-oligonucleotide conjugates, and have recently begun to explore the use of CPP-dendrimer-oligonucleotide complexes. We have found that CPP-antisense oligonucleotide conjugates can be taken up by cells and can effectively modify gene expression in cell culture and in tissues. Although not as potent in cell culture as cationic lipid delivery agents, CPP-oligonucleotide conjugates offer the advantage of being molecules rather than particles, and may have substantial advantages over particle-based delivery in the in vivo setting.

N-sulfonato-N,O-carboxymethylchitosan: A novel polymeric absorption enhancer for the oral delivery of macromolecules

Chitosan has been shown to act on the mucosal epithelial barriers mainly when protonated at acidic pH values in which it is soluble. Soluble chitosan is able to improve the permeation and absorption of neutral to cationic macromolecules only, as it forms polyelectrolyte complexes with anionic macromolecules. LMWH (Low Molecular Weight Heparin) is an anionic polysaccharide finding clinical application as an improved antithrombotic agent compared to Unfractionated Heparin (UFH). In this study we have employed N-sulfonato-N,O-carboxymethylchitosan (SNOCC) as a potential intestinal absorption enhancer of LMWH, Reviparin. SNOCC was prepared at 3 different viscosity grades 20, 40 and 60 cps and identified as SNOCC-20, SNOCC-40 and SNOCC-60, respectively. SNOCC materials were tested in vitro for their ability to decrease the Trans Epithelial Electrical Resistance (TEER) of Caco-2 cell monolayers. They were further tested as transport enhancers of hydrophilic compounds such as (14)C-mannitol, FITC-Dextran (MW 4400 Da) and Reviparin (LMWH). Solutions of Reviparin, with or without SNOCC, were administered intraduodenally in vivo in rats and the absorption of the drug was assessed by measuring the Anti-Xa levels in rat plasma. In vitro studies showed that SNOCC materials were able to induce a concentration dependent decrease in the TEER of the Caco-2 monolayers. SNOCC-40 and -60 were shown to decrease resistance more readily compared to the low viscosity SNOCC-20. (14)C-mannitol permeation data across intestinal epithelia were in agreement with the observed decrease in TEER; the higher viscosity SNOCC-60 was the most effective demonstrating a 51-fold enhancement of the permeation of the radiolabeled marker. Studies with both FITC-Dextran and Reviparin demonstrated significantly increased permeation across Caco-2 cell monolayers when they were co-incubated at the apical side of the monolayer. Intestinal absorption of Reviparin in rats was increased when it was co-administered with SNOCC-40 and -60, in agreement with in vitro data. Anti-Xa levels were elevated to and above the antithrombotic levels and were sustained for at least 6 h, giving an 18.5-fold increase in the AUC of LMWH in rats. In conclusion, SNOCC-40 and -60 have been shown to enhance both permeation and absorption of Reviparin across intestinal epithelia proving their potential as polymeric absorption enhancers.

[The translocation of macromolecules via the hematoencephalic barrier]

The solution to the problem of transportation of high-molecular substances via the hematoencephalic barrier (HEB) is a necessary condition for the development of theoretical and applied aspects of selective transport of biologically active substances (neurotrops, medications) from blood into the brain. In the last decades, views on the possibility of macromolecular transport through intact HEB have changed substantially. Under physiological conditions, translocation of macromolecular substances via HEB is performed with the help of specific molecular transport systems and by endocytosis. The former mechanism prevails both in intensity and the nomenclature of the substances transported. The permeability of the intact (unchanged) HEB for macromolecules exists to an extent necessary for normal CNS functioning. Destruction of dense contacts in the HEB, local retraction and death of endotheliocytes, destruction of the basal membrane take place in pathological processes in the nervous tissue under the influence of inflammatory factors (cytokines, metalloproteinases etc) induced by activated endotheliocytes, T-lymphocytes, macrophages and glial cells; this in fact opens the paracell way for macromolecular components of blood.

Role of Antithrombin and Factor XIII In Leukocyte-Independent Plasma Extravasation During Endotoxemia: An Intravital-Microscopic Study in the Rat

BACKGROUND

Platelet-endothelial interactions have been shown to be main mediators of leukocyte-independent endothelial damage. Besides altering platelet-endothelial interactions, both antithrombin and factor XIII reduce microvascular permeability in leukocyte-dependent experimental models. Thus, it was our aim to investigate the effects of antithrombin and factor XIII on microvascular permeability during leukocyte-independent endotoxemia.

MATERIAL AND METHODS

In male Wistar rats, venular wall shear rate, macromolecular efflux, and leukocyte-endothelial interaction were determined in mesenteric postcapillary venules using intravital microscopy at baseline, 60, and 120 min after the start of the experiment. Fucoidin and a continuous infusion of lipopolysaccharides were used to generate leukocyte-independent endotoxemia. The experiment was divided into two parts 1) an antithrombin study and 2) a factor XIII study.

RESULTS

No differences between groups in leukocyte rolling and venular wall shear rate could be observed in both parts of the experiment. Pretreatment with antithrombin reduced microvascular permeability significantly compared with control subjects (120 min: Fuco [untreated]: 0.14 +/- 0.03; Fuco/ETX [control]: 0.37 +/- 0.06; Fuco + ATIII/ETX: 0.15 +/- 0.02; P < 0.05). Factor XIII reduced microvascular permeability significantly after 60 min (Fuco [untreated]: 0.10 +/- 0.03; Fuco/ETX [control]: 0.36 +/- 0.07; Fuco + FXIII/ETX: 0.13 +/- 0.04; P < 0.05). This effect diminished after 120 min (Fuco [untreated]: 0.12 +/- 0.03; Fuco/ETX [control]: 0.5 +/- 0.08; Fuco + FXIII/ETX: 0.29 +/- 0.05; P < 0.05).

CONCLUSIONS

Antithrombin and factor XIII reduce leukocyte-independent microvascular permeability. Yet, factor XIII also shows a nonprotective effect on a long-term basis. These data emphasize the central role of platelets in leukocyte-independent endotoxemia.

A sensitive in vivo model for quantifying interstitial convective transport of injected macromolecules and nanoparticles

Effective interstitial transport of particles is necessary for injected drug/diagnostic agents to reach the intended target; however, quantitative methods to estimate such transport parameters are lacking. In this study, we develop an in vivo model for evaluating interstitial convection of injected macromolecules and nanoparticles. Fluorescently labeled macromolecules and particles are coinfused with a reference solute at constant infusion pressure intradermally into the mouse tail tip, and their relative convection coefficients are determined from spatial and temporal interstitial concentration profiles. Quantifying relative solute velocity with a coinfused reference solute eliminates the need to estimate interstitial fluid velocity profiles, greatly reducing experimental variability. To demonstrate sensitivity and usefulness of this model, we compare the effects of size (dextrans of 3, 40, 71, and 2,000 kDa and 40-nm diameter particles), shape (linear dextran 71 kDa vs. 69 kDa globular protein albumin), and charge (anionic vs. neutral dextran 3 kDa) on interstitial convection. We find significant differences in interstitial transport rates between each of these molecules and confirm expected transport phenomena, testifying to sensitivity of the model in comparing solutes of different size, shape, and charge. Our data show that size exclusion (within a specific size range) dominates molecular convection, while mechanical hindrance slows larger molecules and nanoparticles; proteins convect slower than linear molecules of equal molecular mass, and negative surface charges increase convection through matrix repulsion. Our in vivo model is presumably a sensitive and reliable tool for evaluating and optimizing potential drug/diagnostic vehicles that utilize interstitial and lymphatic delivery routes.

Supramolecular aggregates of amphiphilic gadolinium complexes as blood pool MRI/MRA contrast agents: physicochemical characterization

In this paper, we present the development of a new potential blood pool contrast agent for magnetic resonance imaging applications (MRA/MRI) based on gadolinium complexes containing amphiphilic supramolecular aggregates. A novel amphiphilic unimer, containing the DTPAGlu chelating agent covalently bound to two C18 alkylic chains, has been synthesized. DTPAGlu is a well-known chelating agent for a wide number of ions such as the paramagnetic metal ion Gd3+ used as contrast agent in MRA/MRI. The wide aggregation behavior of this surfactant, as free base or as gadolinium complex, has been studied and compared by means of dynamic light scattering, small-angle neutron scattering and cryogenic transmission electron microscopy techniques. Near neutral pH in both cases, the dominant aggregates are micelles. The high negative actual charge of the surfactant headgroup causes a strong headgroups repulsion, promoting the formation of large and high curvature aggregates. By decreasing pH and less markedly increasing the ionic strength, we observe a micelle-to-vesicle transition driven by a decreased electrostatic repulsion. A straightforward switch between different aggregation states can be particularly useful in the development of pH-responsive MRA/MRI contrast agents.

Gd-DTPA L-cystine bisamide copolymers as novel biodegradable macromolecular contrast agents for MR blood pool imaging

PURPOSE

The purpose of this study was to synthesize biodegradable Gd-DTPA L-cystine bisamide copolymers (GCAC) as safe and effective, macromolecular contrast agents for magnetic resonance imaging (MRI) and to evaluate their biodegradability and efficacy in MR blood pool imaging in an animal model.

METHODS

Three new biodegradable GCAC with different substituents at the cystine bisamide [R = H (GCAC), CH2CH2CH3 (Gd-DTPA L-cystine bispropyl amide copolymers, GCPC), and CH(CH3)2 (Gd-DTPA cystine bisisopropyl copolymers, GCIC)] were prepared by the condensation copolymerization of diethylenetriamine pentaacetic acid (DTPA) dianhydride with cystine bisamide or bisalkyl amides, followed by complexation with gadolinium triacetate. The degradability of the agents was studied in vitro by incubation in 15 microM cysteine and in vivo with Sprague-Dawley rats. The kinetics of in vivo contrast enhancement was investigated in Sprague-Dawley rats on a Siemens Trio 3 T scanner.

RESULTS

The apparent molecular weight of the polydisulfide Gd(III) chelates ranged from 22 to 25 kDa. The longitudinal (T1) relaxivities of GCAC, GCPC, and GCIC were 4.37, 5.28, and 5.56 mM(-1) s(-1) at 3 T, respectively. The polymeric ligands and polymeric Gd(III) chelates readily degraded into smaller molecules in incubation with 15 microM cysteine via disulfide-thiol exchange reactions. The in vitro degradation rates of both the polymeric ligands and macromolecular Gd(III) chelates decreased as the steric effect around the disulfide bonds increased. The agents readily degraded in vivo, and the catabolic degradation products were detected in rat urine samples collected after intravenous injection. The agents showed strong contrast enhancement in the blood pool, major organs, and tissues at a dose of 0.1 mmol Gd/kg. The difference of their in vitro degradability did not significantly alter the kinetics of in vivo contrast enhancement of the agents.

CONCLUSION

These novel GCAC are promising contrast agents for cardiovascular and tumor MRI, which are later cleaved into low molecular weight Gd(III) chelates and rapidly cleared from the body.

Closomers of High Boron Content: Synthesis, Characterization, and Potential Application as Unimolecular Nanoparticle Delivery Vehicles for Boron Neutron Capture Therapy

Unique nanosized closomers of high boron content that may exhibit potential as boron neutron capture therapy target species have been synthesized. The design of these boron-rich nanospheres is based in part on previous work involving dodeca(carboranyl)-substituted closomers [Thomas, J.; Hawthorne, M. F. Chem. Commun. 2001, 1884-1885]. Coupling of ortho-carborane moieties through ester and ether linkages to the rigid [closo-B(12)(OH)(12)](2-) scaffold resulted in the development of a 12(12)-closomer-ester derivative, dodeca[6-(1,2-dicarba-closo-dodecaboran-1-yl)hexanoate]-closo-dodecaborate (2-), 6, and 12(12)-closomer-ether derivatives, dodeca[6-(2-methy1-1,2-dicarba-nido-dodecaboran-1-yl)hexyl]-closo-dodecaborane (14-), 14, and dodeca[6-(7,8-dicarba-nido-dodecaboran-7-yl)hexyl]-closo-dodecaborane (14-), 15. These closomers were investigated by UV-visible spectroscopy and cyclic voltammetry. Additionally, a deboronation method employing NaCN as the nucleophilic reagent was utilized to obtain sodium salts of the ether-linked nido-closomer polyanions, which were purified using a newly developed size-exclusion high pressure liquid chromatography method.

[Influence of hyaluronan on peritoneal permeability for macromolecules in vitro]

Recent studies pointed out advantages of high-molecular hyaluronic acid (HA) application into dialysis fluids. This molecule is an essential component of peritoneal extracellular matrix. The compound shows antiadhesive properties and participates in restoring of peritoneal integrality and remodeling of peritoneum, which have been changed by prolonged peritoneal dialysis and returning incidents of peritonitis. Influence of HA on transperitoneal transport of large and small molecules is recognized in a little range. The aim of presented studies in vitro was qualification of hyaluronan influence on transport dynamics of the selected macromolecules (albumin 1 g/dL, icodextrin 7.5 g/dL and insulin 0.1 g/dL). Values of the transfer, directed from the interstitial to the mesothelial side of membrane (I-->M) and in the opposite direction (M-->I) were expressed as coefficient of diffusive permeability P [cm/s]. In the case of each macromolecule, two separate research series of the experiments were done. In the first one transperitoneal transport in the control conditions (120 min) was analyzed, and in the secondtransfer parameters before (15-60 min) and after hyaluronan (0.04 g/dL) application on the mesothelial side of peritoneal membrane (75-120 min) were examined. Stability of albumin and insulin transport (in the case of the both transfer directions) and icodextin passage (only M-->I direction) was observed in the presented studies when we compare the first and the second hours of the experiments. In the opposite direction (I-->M) it was showed an increase of its transport with time by about 50%. The mean values of P +/- SEM amounted to 0,271 +/- 0,056 [x10(-4); cm/s] and 0,315 +/- 0,057 [x10(-4); cm/s] for albumin and 0,145 +/- 0,033 [x10(-4); cm/s] and 0,146 +/- 0,022 [x10(-4); cm/s] for insulin, respectively in the case of I-->M and M-->I directions and 0,194 +/- 0,035 [x10(-4); cm/s] for icodextrin transfer directed from the mesothelial to the interstitial side of membrane. In the opposite direction (I-->M) values of P coefficient amounted to: 0,280 +/- 0,038 [x10(-4); cm/s] in the first experimental hour, and 0,394 +/- 0,046 [x10(-4); cm/s] in the second one. It was observed also asymmetry of glucose polymer passage with I-->M transfer domination. Hyaluronan eliminated this asymmetry. After use this compound the transport parameters of icodextrin were stable for the both I-->M and M-->I directions. Hyaluronan did not change values of diffusive permeability coefficients P in the case of bidirectional transfer of albumin and insulin. The obtained results show, that values of macromolecules transfer across peritoneum in vitro don't depend on their molecular weight and isoelectric points. Dynamics of albumin and insulin transperitoneal passage is stable. Icodextrin transport, directed from the interstitial to the mesothelial side of membrane, predominates transfer in the opposite direction. Hyaluronan modifies dynamics of transperitoneal icodextrin passage, but doesn't influence on permeability of the membrane in the case of albumin and insulin.

Methotrexate-modified superparamagnetic nanoparticles and their intracellular uptake into human cancer cells

A magnetic nanoparticle conjugate was developed that can potentially serve both as a contrast enhancement agent in magnetic resonance imaging and as a drug carrier in controlled drug delivery, targeted at cancer diagnostics and therapeutics. The conjugate is made of iron oxide nanoparticles covalently bound with methotrexate (MTX), a chemotherapeutic drug that can target many cancer cells whose surfaces are overexpressed by folate receptors. The nanoparticles were first surface-modified with (3-aminopropyl)trimethoxysilane to form a self-assembled monolayer and subsequently conjugated with MTX through amidation between the carboxylic acid end groups on MTX and the amine groups on the particle surface. Drug release experiments demonstrated that MTX was cleaved from the nanoparticles under low pH conditions mimicking the intracellular conditions in the lysosome. Cellular viability studies in human breast cancer cells (MCF-7) and human cervical cancer cells (HeLa) further demonstrated the effectiveness of such chemical cleavage of MTX inside the target cells through the action of intracellular enzymes. The intracellular trafficking model proposed was supported through nanoparticle uptake studies which demonstrated that cells expressing the human folate receptor internalized a higher level of nanoparticles than negative control cells.

Characterization of the influence of nitric oxide donors on intestinal absorption of macromolecules

To characterize the influence of nitric oxide (NO) donors on the intestinal absorption of macromolecules, the relationship between the release rate of NO from NO donors and their absorption-enhancing effects and the effects of several scavengers and generators on the absorption-enhancing effects of NO donor were investigated. The t1/2 values of the NO release rate from 3-(2-hydroxy-1-methylethyl-2-nitrosohydrazino)-1-propanamine (NOC5), 3-(2-hydroxy-1-methylethyl-2-nitrosohydrazino)-N-methyl-1-propanamine (NOC7) and N-ethyl-2-(1-ethyl-hydroxy-2-nitrosohydrazino)-ethanamine (NOC12) are 25, 5 and 100min, respectively. The absorption-enhancing effects of NO donors on the absorption of fluorescein isothiocyanate dextrans with an average molecular weight of 4400 (FD-4) are NOC5 > NOC7 > NOC12 in the colon. The lowest enhancing effect of NOC12 may be due to the slow rate of NO release. The enhancing effect of NOC7 rapidly disappeared compared with the effect of NOC5. The results raise the possibility that the difference between NOC5 and NOC7 on enhancing effect is related to the t1/2 of the NO release. The NOC7-induced enhancing effect was prevented by the co-administration of 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazole-1-oxyl-3-oxide sodium salt (C-PTIO), an NO scavenger; tiron, an O2(-) scavenger; mannitol, an OH* scavenger, and deferoxamine, peroxynitrate scavenger. Pyrogallol, an O2(-) generator, potentiated the NOC7-induced enhancing effect. These results support a role for peroxynitrate, and possibly OH*, in the NO donor-induced intestinal enhancing effect.

Endoscopic biopsies in Ussing chambers evaluated for studies of macromolecular permeability in the human colon

OBJECTIVE

Studies of mucosal permeability to protein antigens in humans are limited to in vitro techniques. The use of surgical specimens for such studies has major shortcomings. Endoscopic biopsies in Ussing chambers have been introduced as a means of studying secretion and transepithelial permeability, but have not been evaluated for studies of protein antigen uptake in human intestine.

MATERIAL AND METHODS

Standard forceps biopsies from the sigmoid colon of 24 healthy volunteers were mounted in Ussing chambers with an exposed tissue area of 1.76 mm2. 51Cr-EDTA (paracellular probe) and horseradish peroxidase (HRP; 45 kDa protein antigen) were used as permeability markers. Mucosal permeability, electrophysiology, histology and energy contents of the biopsies were studied over time. To evaluate the ability of the technique to detect permeability changes, the mucosa was modulated with capric acid, a medium-chain fatty acid, known to affect tight junctions.

RESULTS

In the Ussing chamber the mucosal biopsies were viable for 160 min with stable levels of ATP and lactate, and only minor changes in morphology. Steady-state permeability with low variability was seen for both markers during the 30-90 min period. Exposure to capric acid induced a rapid decrease in short-circuit current (Isc) and a slower reversible decrease in transepithelial resistance (TER), as well as an increased permeability to 51Cr-EDTA and HRP.

CONCLUSIONS

Endoscopic biopsies of human colon are viable in Ussing chambers and are reliable tools for studies of mucosal permeability to protein antigens. The technique offers a broad potential for studies of mucosal function in the pathophysiology of human gastrointestinal diseases.

Smart polymeric carriers for enhanced intracellular delivery of therapeutic macromolecules

Limited cytoplasmic delivery of enzyme-susceptible drugs remains a significant challenge facing the development of protein and nucleic acid therapies that act in intracellular compartments. Researchers have examined several approaches, including fusogenic proteins and protein transduction domains, to enhance the intracellular delivery of the therapeutic cargo. This review summarises efforts to develop 'smart' pH-sensitive and membrane-destabilising polymers that can shuttle therapeutic peptide, protein and nucleic acid molecules past the endosomal membrane into the cytoplasm of targeted cells. Several classes of 'smart' non-degradable polymeric carriers have been developed that have proved effective both in vitro and in vivo in enhancing the cytoplasmic delivery of a variety of therapeutic molecules.

The effect of cholate on solubilisation and permeability of simple and protein-loaded phosphatidylcholine/sodium cholate mixed aggregates designed to mediate transdermal delivery of macromolecules

Carriers for non-invasive administration of biologically important antioxidant enzymes Cu,Zn-superoxide dismutase (SOD) and catalase (CAT) were developed. Solubilisation and permeabilities of various soybean phosphatidylcholine/sodium cholate (SPC/NaChol) mixtures, mainly in the form of lipid bilayers, focussing on system properties relevant for non-invasive enzyme delivery were investigated in this work. Static and dynamic light scattering measurements gave information on the behaviour of the systems containing up to 40 mM NaChol and 30.6-1.2 mM SPC in the final suspension. The average size of such mixed aggregates was in the 100-200 nm range. Suspension turbidity decreased by 50% upon increasing nominal molar detergent/lipid ratio to NaChol/SPC = 7 and 1.25, in case of SPC = 1.2 and 19.6 mM, respectively. The effective NaChol/SPC molar ratio in bilayers saturated with the detergent was found to be: R(e)(sat) = 0.70 +/- 0.01; bilayer solubilisation point corresponded to R(e)(sol) = 0.97 +/- 0.02, independently of enzyme loading. Vesicles became very permeable to SOD when membrane bound NaChol concentration exceeded 13.7 mM, in case of total starting lipid concentration of 138 mM diluted to SPC = 19.6 mM. Specifically, we measured a 50% loss of SOD from the vesicles with an aggregate-associated molar detergent ratio NaChol/SPC approximately 0.7, which is near the saturation but well below the solubilisation limit. Calcein efflux from such vesicles was compared with SPC/NaChol/SOD mixed aggregates. Our results should contribute to the future design of vesicle mediated transdermal delivery of antioxidant enzymes.

Dendrimer-based nanosized MRI contrast agents

Paramagnetic metals can induce T1 shortening by interaction with free water molecules. Two metal ions, Gadolinium and Manganese, are currently available for human use. Gadolinium-based MRI contrast agents (CAs) can operate using a approximately 100-fold lower concentration of Gadolinium ions in comparison to the necessary concentration of Iodine atoms employed in CT imaging in the tissues. Therefore, numerous macromolecular MRI CAs prepared employing relatively simple chemistry are readily available that can provide sufficient enhancement for multiple applications. Herein, we describe the synthesis, characteristics, and potential applications of dendrimer-based macromolecular MRI CAs in our recently reported libraries. This entire series of dendrimer-based macromolecular MRI CAs have a spherical shape and possess similar surface charges. Changes in molecular size altered the route of excretion. Smaller sized contrast agents, of less than 60 kD molecular weight, were excreted through the kidney resulting in these agents being potentially suitable as functional renal contrast agents. Less hydrophilic and larger sized contrast agents were found better suited for use as blood pool contrast agents. Hydrophobic variants of CAs formed with polypropylenimine diaminobutane dendrimer cores quickly accumulated in the liver and can function as liver contrast agents. Larger hydrophilic agents are also useful for lymphatic imaging. Finally, contrast agents conjugated with either monoclonal antibodies or with avidin are able to function as tumor-specific contrast agents and might also be employed as therapeutic drugs for either gadolinium neutron capture therapy or in conjunction with radioimmunotherapy.

Oligonucleotide delivery to tumours using macromolecular carriers

Microparticles have been used for delivery of chemo- and radio-therapeutic agents to tumours in patients for more than a decade, whereas cationic liposomes have been used for introducing nucleic acids into mammalian cells for the same period of time. This minireview discusses the potential of delivering therapeutic ONs (oligonucleotides) to tumours using cationic liposomes and the major obstacles to such delivery. It also proposes how microparticles can be utilized for delivery of ONs to solid tumours. Prospects for improved ON delivery using these carriers and ways to achieve this are discussed.

Supramolecular Gene Delivery Vectors Showing Enhanced Transgene Expression and Good Biocompatibility

Soluble supramolecular inclusion complexes were formed by threading alpha-cyclodextrin (alpha-CD) molecules over poly(ethylene glycol) (PEG) and poly(epsilon-caprolactone) (PCL) chains of ternary block copolymers of PEG, PCL and polyethylenimine (PEI). Characteristic shifts of PCL absorptions in FTIR, (1)H NMR and UV spectra strongly suggest that alpha-CD is threaded over PEG and PCL blocks. Due to the reduced hydrophobic interaction between PCL blocks, the resulting supramolecular complexes displayed a dramatically increased solubility, in comparison with the ternary block copolymers. Their ability to complex DNA was almost as efficient as that of branched PEI 25 kDa, as shown in the ethidium bromide fluorescence quenching experiments. Resulting DNA polyplexes displayed a size of around 200 nm and a neutral surface charge. Microscopy studies in 3T3 fibroblasts revealed an efficient cellular uptake. Transfection efficiencies of inclusion complexes were in the same order of magnitude as PEI. In contrast to PEI a 100x lower toxicity was observed by MTT-assay, allowing the administration of nitrogen-to-phosphate ratios of up to 20. These new gene delivery systems merit further characterization under in vivo conditions.

Synthesis and in vitro evaluation of macromolecular antitumour derivatives based on phenylenediamine mustard

Poly-[N-(2-hydroxyethyl)-L-glutamine] (PHEG) and poly(ethylene glycol) (PEG)-grafted PHEG conjugates of N,N-di(2-chloroethyl)-4-phenylenediamine mustard (PDM) were synthetised. A collagenase-sensitive oligopeptide spacer was selected to link the cytotoxic agent PDM onto the polymeric carrier. First, the oligopeptide-drug conjugate, L-pro-L-leu-gly-L-pro-gly-PDM, was prepared. In a second step, the low molecular weight PDM derivative and PEG-NH(2) were coupled to a N,N-disuccinimidylcarbonate activated PHEG. Dynamic laser light scattering measurements indicated the formation of aggregates. The presence of human serum albumin had no significant effect on the diameter of the conjugates. The hydrolytic stability of the conjugates was investigated in buffer solutions. The conjugates showed an improved stability compared to the parent nitrogen mustard. The enzymatic degradation studies of the polymeric conjugates were performed in the presence of collagenase type IV (Clostridiopeptidase A; EC 3.4.24.3), cathepsin B (EC 3.4.22.1), cathepsin D (EC 3.4.23.5) and tritosomes. Only the bacterial collagenase type IV was able to cleave the spacer releasing free PDM and its peptidyl derivative, gly-L-pro-gly-PDM. The in vitro cytotoxicity of the conjugates was evaluated against HT1080 fibrosarcoma cells and MDA adenocarcinoma cells. All conjugates showed low toxicity towards these cell lines.

Effect of withholding macromolecules on the duration of intestinal permeability to colostral IgG in foals

OBJECTIVE

To quantify absorption of colostral IgG by healthy neonatal foals and to test the hypothesis that delayed ingestion of macromolecules prolongs the duration of intestinal permeability to immunoglobulins (Ig) in newborn foals.

ANIMALS

Thirteen mixed breed foals.

PROCEDURE

Foals were randomly assigned to two treatment groups, which were fed either a glucose-electrolyte solution or a commercial milk replacer for 12 h after birth, before being fed a known amount of colostral IgG. A control group was fed a known amount of colostral IgG from birth. The efficiency of IgG absorption was calculated following determination of plasma IgG concentration for each foal.

RESULTS

Foals given colostrum immediately after birth transferred approximately 51% of ingested IgG into their vascular space. Delayed colostral ingestion significantly reduced the amount of IgG absorbed by foals. Withholding macromolecules for 12 h had no effect on the subsequent efficiency of IgG absorption.

CONCLUSIONS

Colostrum should be supplied to foals within 12 h of birth for best uptake of Ig. The type of fluid administered to foals before the ingestion of colostrum does not influence subsequent absorption of Ig, suggesting that the process of gut closure in foals is not mediated by a finite capacity for macromolecular uptake.

Oral delivery of macromolecules using intestinal patches: applications for insulin delivery

Oral drug delivery, though attractive compared to injections, cannot be utilized for the administration of peptides and proteins due to poor epithelial permeability and proteolytic degradation within the gastrointestinal tract. A novel method is described that utilizes mucoadhesive intestinal patches to deliver therapeutic doses of insulin into systemic circulation. Intestinal patches localize insulin near the mucosa and protect it from proteolytic degradation. In vitro experiments confirmed the secure adhesion of patches to the intestine and the release of insulin from the patches. In vivo experiments performed via jejunal administration showed that intestinal insulin patches with doses in the range of 1-10 U/kg induced dose-dependent hypoglycemia in normal rats with a maximum drop in blood glucose levels of 75% observed at a dose of 10 U/kg. These studies demonstrate that reduction in blood glucose levels comparable to that induced by subcutaneous injections can be achieved via enteral insulin absorption with doses only 2-10-fold higher than subcutaneous doses.

A biophysical approach to capillary permeability

In this preliminary report, the capillary leakage that occurs after scald injury is considered a biophysical phenomenon and is treated by sealing the "pores," or endothelial gaps, in the capillary membranes with biodegradable macromolecules of the appropriate size and shape. We have measured albumin leakage from standardized scald burns in the rat jejunum with and without variously sized fractions of intravenous macromolecules of hydroxyethyl starch (HES) used as a sealing agent. The observed reduction of albumin leakage from injured capillaries was attributed to the sealing effect. The fraction HES (Fm) with molecular weights of 100,000 to 300,000 daltons performed significantly better (p less than 0.05) as a sealing agent when compared with HES (F1) fraction molecular weights of 300,000 to 3.4 million daltons, HES (Fs) molecular weight less than 50,000 daltons, and two control groups receiving the intravenous Ringer's lactate solution or serum albumin 5%. This capillary sealing phenomenon was shown to be independent of colloid osmotic pressure effect. It is believed to be related to the size and the shape of the noncharged macromolecules.

On the time-dependent diffusion of macromolecules through transient open junctions and their subendothelial spread. I. Short-time model for cleft exit region

In this two-part study we shall quantitatively study, using time-dependent models, the hypothesis that transient open junctions associated with widely scattered endothelial cells undergoing mitosis are the structural equivalent for the large pore pathway via which macromolecules the size of albumin or larger cross the vascular endothelium. In an earlier steady-state model [Am. J. Physiol. 248, H945-960 (1985)], the authors demonstrated that such an open-junction pathway could quantitatively account for the regional differences in macromolecular permeability observed in various mammalian arteries in regions of enhanced cell turnover as indicated by 3H-thymidine although these cells were less than 1% of the population and the open junctions occupied less than 10(-5) of the endothelial surface. The time-dependent models described herein have been used to identify a time window and size of probe molecule wherein this hypothesis could be tested experimentally in the larger blood vessels. The first stages of these experiments have now been completed and provide convincing evidence that the junctions of virtually all endothelial cells in the M phase of the cell cycle are leaky to macromolecules (Lin et al., 1988). The statistical frequency of such leakage sites has also been determined. The time-dependent models developed herein contain two important refinements that were not contained in the earlier steady state model. First the finite resistance of the open cleft as a function of molecular size is accounted for by introducing a diffusion coefficient ratio Dj/Dz describing the relative resistance of the open cleft compared to the subendothelial tissue in the direction normal to the endothelial surface. Second the non-isotropy of the vessel wall due to the elastic lamina is considered by introducing a second diffusion coefficient ratio Dx/Dz describing the relative resistance in the lateral as compared to the normal direction. This second ratio can be as large as 100 for the arterial intima, but is of order unity for capillaries. In Part I a short time model is presented to describe the initial labeling of the open cleft and the subendothelial space in the vicinity of the cleft exit following the introduction of a tracer macromolecule. This model is valid for both larger vessels and capillaries since wall thickness and curvature and the interaction between leakage sites does not enter into the model description. In Part II (Wen et al., 1988) a long-time model is developed for larger vessels only which is valid for greater times including steady-state labeling.