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Biomedical subjects

W M Saltzman

Publications and source records attributed to W M Saltzman.

At least 55 records · Page 3Linked to original sources
PubMed1996

Oral immunization with an anti-idiotypic antibody to the exoglycolipid antigen protects against experimental Chlamydia trachomatis infection.

Chlamydia trachomatis is the leading cause worldwide of preventable infectious blindness (trachoma) and sexually transmitted disease, including nongonoccocal urethritis and pelvic inflammatory disease. To date, no effective vaccine against C. trachomatis infection has been identified. A monoclonal anti-idiotypic antibody (anti-Id) to the chlamydial exoglycolipid antigen (GLXA) was tested in a murine model of ocular chlamydial infection for its ability to induce systemic immunity, which reduces microbiologic and clinical disease. The anti-Id to GLXA, delivered either systemically in soluble form or orally after encapsulation in poly(lactide) microspheres, induced significant protective immunity against ocular challenge of mice with a human biovar of C. trachomatis. Protection was associated with induction of anti-GLXA antibody and anti-chlamydial neutralizing antibody.

Administration, Oral↗
PubMed1996

Residence half-life of IgG administered topically to the mouse vagina.

Antibodies delivered directly to the vagina can provide passive immunoprotection against pregnancy and sexually transmitted disease. The duration of protection is limited by the residence time of the antibodies in the vagina; to our knowledge such residence times have not been reported. We investigated the time-course of disappearance of IgG delivered to the mouse vagina using three different methods to monitor the amount of administered IgG remaining in the vagina: gamma counting of 125I-IgG, viral neutralization of unlabeled monoclonal anti-herpes virus IgG2a, and ELISA of biotinylated IgG. The test IgG was delivered to the vagina in saline and recovered by lavage. All three methods yielded similar results, suggesting that the residence half-life is not significantly affected by the volume administered, phase of the estrous cycle, or labeling of IgG. In awake mice, a significant fraction of IgG disappeared with a relatively short half-life, (t1/2)alpha, of 0.7 +/- 0.1 h; but this rapid (alpha phase) decrease did not occur in anesthetized mice, suggesting that the movements of awake mice expel some of the test IgG-saline solution from the vagina. Over the next 25 h, the test IgG disappeared with a residence half-life, (t1/2)beta, of 5 +/- 2 h. We believe this slow elimination of IgG may depend on the rate that mucus secretions are shed from the vagina.

Administration, Topical↗
PubMed1996

Stabilization of nerve growth factor in controlled release polymers and in tissue.

We have studied the release of nerve growth factor (NGF), a protein under consideration for treatment of Alzheimer's Disease, from polymer matrices and microspheres to characterize the stability of NGF, the dynamics of NGF release, and the distribution of NGF within the brain interstitium. Poly(ethylene-co-vinyl acetate) (EVAc) disks and poly(L-lactic acid) (PLA) microspheres were formed by codispersing NGF with one of a variety of molecules. The mass of mouse NGF (mNGF) detected following release from EVAc disks into buffered saline varied five-fold over the range of codispersants studied, with carboxymethyldextran providing optimal release, while the mass of recombinant human NGF (rhNGF) released varied four-fold from both EVAc disks and PLA microspheres, with albumin and carboxymethyldextran providing optimal release. Variation of the codispersant species significantly affected NGF release into buffered saline; it also had a noticeable, but small, effect of the amount of NGF found in the brain tissue following implantation of a polymer device. To improve NGF retention in tissue, NGF was conjugated to 70,000 molecular weight dextran and incorporated into a polymeric device. The distribution of NGF was enhanced by conjugation; comparison of NGF concentrations in the brain to a mathematical model of diffusion and elimination suggested that the elimination rate of NGF-dextran conjugate in the tissue was over seven times slower than the elimination rate of NGF. These results indicate that variation of the properties of the controlled release system may be useful in regulating the time course of NGF delivery to tissue, and that modification of the NGF itself can improve penetration and retention in the brain.

Animals↗
PubMed1996

Novel systems for controlled delivery of macromolecules.

Gene therapy promises new treatments for human disease by alterations in the DNA content of tissues. Methods for efficient and stable introduction of genes into target cells in the body are critically important in this effort. Researchers and physicians now have many years of experience with synthetic polymers for controlled drug delivery; many of these polymers can also be used to deliver macromolecules at controlled rates to tissues. This article reviews the use of polymers in controlled protein delivery and suggests ways that polymer delivery systems may be useful in the delivery of gene transfer agents.

Animals↗
PubMed1995

Distribution of nerve growth factor following direct delivery to brain interstitium.

Several studies suggest the potential of nerve growth factor (NGF) in the treatment of patients with Alzheimer's disease. To characterize NGF transport within the brain interstitium, we implanted controlled release polymers containing NGF and [125I]NGF into the brains of adult male rats and measured spatial distributions of NGF for up to one week. NGF concentration in the brain was quantified using ELISA, radiation counting, and autoradiography. At 2 days post-implantation, quantities of NGF in excess of 50 pg per section were detected within thick (1 mm) coronal slices of the hemisphere ipsilateral to the site of implantation up to 3 mm rostral and caudal to the edge of the polymer. Lower levels of radioactivity (> 5 pg but < 50 pg NGF per section) could be detected throughout the rest of the brain. Levels were highest in the tissue sections containing the polymer, reaching 9.5 ng per section. Autoradiography of thin (20 microns) coronal sections indicated that local NGF concentrations immediately adjacent to the polymer approached 40 micrograms/ml. Analysis of sequential sections on the autoradiograph confirmed that NGF was transported only 2-3 mm from the polymer in any direction. At one week post-implantation, the pattern of NGF distribution was similar to that seen at 2 days, and concentrations remained high near the site of the implant. Comparison of local NGF concentration profiles to simple models of diffusion with first-order elimination suggests that the NGF moved through the tissue by diffusion through the interstitial space with a half-life on the order of 0.5 h. The limited range of NGF transport in brain tissue indicates that: (i) protein drug agents such as NGF will probably need to be delivered almost directly to the site of action for efficacy; and (ii) toxicities associated with delivery of NGF and other protein agents to non-target cells, as often occurs with systemic delivery of drugs, may be reduced by local, interstitial delivery since therapy can be restricted to a small volume of the brain.

Animals↗
PubMed1995

Distribution of drugs following controlled delivery to the brain interstitium.

Intracranial controlled release polymers have been used for drug delivery to the brain, bypassing the blood brain barrier (BBB). By understanding the rates and patterns of transport in the local tissues, it is possible to design delivery systems that provide the optimal spatial and temporal pattern of chemotherapy within the intracranial space. This paper reviews the kinetics of drug release from polymeric controlled release implants, and describes the fate of drug molecules following release into the brain interstitium. Potential improvements in drug delivery based on the understanding of the mechanisms of drug release, transport and elimination are discussed.

Animals↗
PubMed1995

Distribution of 1,3-bis(2-chloroethyl)-1-nitrosourea and tracers in the rabbit brain after interstitial delivery by biodegradable polymer implants.

Intracranial tumors, such as glioblastoma multiforme and astrocytomas, are among the most aggressive and difficult to cure. In the present study, we evaluated the intracranial distribution of released agents during the first 3 days after implantation. Polymer implants containing [3H]-1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU), [3H]dextran (MW 70,000) or [14C]iodoantipyrene (IAP) were implanted into the brains of rabbits; autoradiography was used to measure the distribution of radiolabels within the brain at 6, 24 and 72 hr after implantation. For all of the agents studied, the majority of the radioactivity was found within the region 1 to 2 mm from the surface of the polymer. Dextran, however, penetrated farther into the brain than either IAP or BCNU. The distribution of radiolabel on an anteroposterior axis was determined by examining serial coronal images: after 72 hr, significant radioactivity (< 2 S.D. above background) extended > 17 mm in animals with [3H]dextran implants and approximately mm in animals receiving [3H]BCNU or [14C]IAP. Concentration profiles were also measured on coronal images obtained at the implant site: radioactivity dropped to a 10% maximum value 1.7 mm from the surface of the pellet in [3H]dextran-treated animals and < 1.2 mm in [3H]BCNU or [14C]IAP-treated animals. Measured concentration profiles near the polymer were compared to mathematical models of drug diffusion and elimination. These results demonstrate that the majority of agents delivered into the brain by intracranially implanted polymers accumulates in the tissue within 1 to 2 mm of the implant, but that the size of the treated region depends on physicochemical properties of the agents.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1994

Covalent coupling of methotrexate to dextran enhances the penetration of cytotoxicity into a tissue-like matrix.

For antitumor agents introduced directly into the intracranial space, the extent of penetration into tissue, and hence the effectiveness of therapy, depends on the rate of drug elimination from the tissue. To test the hypothesis that slowly eliminated agents would penetrate further through tissues, methotrexate (MTX)-dextran conjugates were produced by covalently linking MTX to dextran through a short-lived ester bond (MTX-ester-dextran; t1/2 approximately 3 days in buffered saline) and a longer-lived amide bond (MTX-amide-dextran; t1/2 > 20 days in buffered saline). The ability of these agents to kill cells and to penetrate through tissue was evaluated using: (a) human brain tumor (H80) cells in a standard format; (b) H80 cells in a novel three-dimensional format that mimics many characteristics of intracranial tumors; and (c) 9L gliosarcoma in the rat brain. Penetration into three-dimensional tissue-like matrices was performed by suspending H80 cells in agarose gels within a hollow fiber that was permeable to MTX but not dextran and injecting MTX or MTX-dextran conjugates into one end of the fiber. The cytotoxicity of MTX-ester-dextran and MTX-amide-dextran against H80 was equivalent to unmodified MTX (50% inhibitory concentration, approximately 0.01 microgram/ml). When released from a biodegradable polyanhydride polymer matrix, MTX and MTX-dextran conjugates retained their ability to inhibit dihydrofolate reductase activity. When MTX or MTX-dextran was diffused into the three-dimensional tumor cell matrix for 10 days, cytotoxic activity penetrated > 2 cm for MTX-amide-dextran and approximately 1 cm for MTX or MTX-ester-dextran; this enhanced penetration correlated with the stability of the MTX-dextran linkage. Intracranial polymeric delivery of MTX or MTX-amide-dextran to rats with intracranial 9L gliosarcoma produced modest but significant increases in survival; conjugation of MTX to dextran appeared to shift the dose-response curve to a lower dosage.

Animals↗
PubMed1994

Leukocytes migrate through three-dimensional gels of midcycle cervical mucus.

The migration of leukocytes through mucus must be an essential factor in the mucosal immune response, particularly during mucosal invasion by pathogens. We used two methods to evaluate the ability of neutrophils to migrate through human midcycle cervical mucus: (i) direct visualization of cell migration within freshly collected mucus samples and (ii) quantification of cell penetration through a layer of mucus overlying a monolayer of cultured intestinal epithelial cells from the T84 cell line. Neutrophils migrated rapidly through human midcycle cervical mucus: the random motility coefficient (mu) ranged from 1.2 to 5.6 x 10(-8) cm2/sec in different mucus samples. The rate and pattern of neutrophil migration in cervical mucus were identical to those in a structurally similar collagen gel (0.4 mg/ml). Therefore, we also quantitatively examined the migratory behavior of human neutrophils, monocytes, and lymphocytes from peripheral blood, as well as leukocytes isolated from semen, in collagen gels as a model of cell migration in cervical mucus. In the absence of stimulation, mu was approximately 10(-8) cm2/s for neutrophils and lymphocytes; monocytes and seminal leukocytes were immotile. In all cases, mu increased with the addition of FMLP. Furthermore, neutrophils were able to penetrate layers of mucus overlying monolayers of T84 cells when the gel thickness was less than approximately 500 microns. These results suggest that leukocytes migrate effectively through mucus, a process which may be related to their ability to function in the mucosal immune system or to serve as vectors for the translocation of infectious pathogens like HIV.

Cell Movement↗
PubMed1994

Antibody diffusion in human cervical mucus.

The mucosal immune system actively transports large quantities of antibodies into all mucus secretions, and these secreted antibodies help prevent infectious entry of many pathogens. Mucus is generally thought to protect epithelial cells by forming a diffusional barrier through which only small molecules can pass. However, electron microscopy indicates that the pore size in mucus is approximately 100 nm, which suggests that antibodies as well as other large molecules might also diffuse through mucus. We measured the diffusion coefficients for antibodies and other proteins within human midcycle cervical mucus using two techniques: fluorescence imaging of concentration profiles and fluorescence photobleaching recovery. The two techniques are complementary, since the rates of diffusion are observed over millimeter distances with fluorescence imaging of concentration profiles and micron distances with fluorescence photobleaching recovery. Both methods yielded essentially the same diffusion coefficients. In contrast to previous reports indicating mucus significantly impedes diffusion of small molecules, antibody diffusion in mucus was relatively unimpeded. In our observations IgG, IgG fragments, IgA, and IgM diffused almost as rapidly in cervical mucus as in water (1.0 > Dmucus/Dwater > 0.7). Simple models for diffusion through water-filled pores suggest that the hydrodynamic pore size for cervical mucus is approximately 100 nm, smaller than the approximately 1000 nm pore size of a collagen gel (at 1 mg/ml) and larger than the approximately 10 nm pore size of gelatin (at 100 mg/ml). This estimated pore size is consistent both with electron micrographs and geometric models of interfiber spacing. Based on these results, we predict that particles as large as viruses can diffuse rapidly through human midcycle cervical mucus, provided the particle forms no adhesive interactions with mucus glycoproteins.

Antibodies↗
PubMed1994

Cell-binding peptides conjugated to poly(ethylene glycol) promote neural cell aggregation.

We have developed a method for promoting cell aggregation with bifunctional macromolecules synthesized by coupling cell-binding peptides to an inert, water-soluble polymer. The peptides Arg-Gly-Asp (RGD) and Tyr-Ile-Gly-Ser-Arg (YIGSR) were conjugated through their amino termini to both ends of linear poly(ethylene glycol) (PEG), producing bifunctional hybrid polymers: RGD-PEG-RGD and YIGSR-PEG-YIGSR. RGD-PEG-RGD promoted aggregation of mechanically-dissociated fetal brain cells, pheochromocytoma cells (PC12), and neuroblastoma cells maintained in rotation culture at 37 degrees C. Enhanced aggregation was noticeable within 10 minutes and became more pronounced over the next several hours: after 7-9 hours, the mean aggregate volume was up to 10 times larger than the mean volume produced in suspensions containing unmodified PEG. Similar results were obtained with YIGSR-PEG-YIGSR and PC12 cells. Enhancement in aggregation correlated with the ability of soluble RGD or YIGSR to inhibit cell adhesion to surfaces coated with laminin or fibronectin. This method for promoting aggregation may be useful for large scale culture of anchorage dependent cells, eliminating the need for microcarriers. In addition, aggregates formed by this method may be suitable for use in artificial organs or as cell transplants for tissue regeneration.

Adrenal Gland Neoplasms↗
PubMed1994

Controlled release of macromolecules from a degradable polyanhydride matrix.

Polymeric matrices that slowly release macromolecules may be useful for the controlled delivery of proteins or polymer-drug conjugates for targeted drug delivery. Solid particles of fluorescein and fluorescently-labeled, size-fractionated dextran (4000-150,000 number average molecular weight) were dispersed in degradable polyanhydride matrices composed of a 1:1 copolymer of fatty acid dimers and sebacic acid. The release of macromolecules from the polymer matrix into buffered saline was measured; changes in the polymer during immersion were monitored by infrared spectroscopy, differential scanning calorimetry, and scanning electron microscopy. Although significant hydrolysis of the polymer occurred within the first day, the matrices remained intact and water-soluble tracers were slowly released for several days. During polymer hydrolysis and erosion, micron-sized pores developed throughout the 2 mm thick polymer matrix, permitting water penetration into the matrix and tracer diffusion out of the matrix. The rate of tracer release from the matrix depended on tracer particle size; rates of fluorescein isothiocyanate dextran release were controlled by adjusting the size of particles dispersed in the matrix.

Biodegradation, Environmental↗
PubMed1993

Antibodies for treating and preventing disease: the potential role of polymeric controlled release.

Following the identification of antibodies (Abs) as agents of immunity, it was hypothesized that individuals could be both (1) protected against disease by the transfer of unmodified Ab (passive immunization), and (2) cured of established disease by Ab armed with cytotoxic agents (immunotherapy). The development of monoclonal antibody (mAb) technology in 1975 reinvigorated these ideas. Although passive immunization has been practiced with great success for many years, successful tissue targeting by systemically delivered immunotoxins in humans has been documented in only a few cases. New modes of drug delivery, engineered for mAb-based products, may enable new applications of passive immunization and may provide improved tissue targeting for immunotherapy. By allowing sustained and tissue-localized delivery of mAb-conjugates, controlled-release polymers may play an important role in this effort. This article reviews the use of mAb in treating and preventing human disease, as well as the pharmacokinetics of Ab delivery. Two areas where controlled Ab release may yield new therapies are highlighted: sustained passive immunization of the mucus secretions and immunotherapy of brain tumors.

Animals↗
PubMed1992

Three-dimensional cell cultures mimic tissues.

Three-dimensional cell culture using gels of type I collagen is a flexible method for studying cell behavior in a tissuelike environment. With only small changes in the basic protocol, we were able to encapsulate neutrophils, hepatocytes, and PC12 cells. As demonstrated by cell-specific assays for migration, protein secretion, and growth factor induction, the encapsulated cells were viable and functional. In future studies, we will focus on using these cell cultures to study cell movement, cell growth, and cell function in carefully controlled tissuelike environments.

Animals↗
PubMed1992

Quantification of human neutrophil motility in three-dimensional collagen gels. Effect of collagen concentration.

Leukocytes must migrate through tissues to fulfill their role in the immune response, but direct methods for observing and quantifying cell motility have mostly been limited to migration on two-dimensional surfaces. We have now developed methods for examining neutrophil movement in a three-dimensional gel containing 0.1 to 0.7 mg/ml rat tail tendon collagen. Neutrophil-populated collagen gels were formed within flat glass capillary tubes, permitting direct observation with light microscopy. By following the tracks of individual cells over a 13.5-min observation period and comparing them to a stochastic model of cell movement, we quantified cell speed within a given gel by estimating a random motility coefficient (mu) and persistence time (P). The random motility coefficient changed significantly with collagen concentration in the gel, varying from 1.6 to 13.3 x 10(-9) cm2/s, with the maximum occurring at a collagen gel concentration of 0.3 mg/ml. The methods described may be useful for studying tissue dynamics and for evaluating the mechanism of cell movement in three-dimensional gels of extracellular matrix (ECM) molecules.

Biophysical Phenomena↗
PubMed1992

Controlled antibody delivery systems.

We have developed methods for controlling the release of antibodies (Ab) from biocompatible polymers. Human Ab, human Ab fragments, and mouse monoclonal antibody (mAb) directed against human chorionic gonadotropin (anti-hCG) were incorporated into matrices of poly(ethylene-co-vinyl acetate), which is stable in biological environments. Human Ab and bovine gamma-globulin were also incorporated in biodegradable matrices of a poly-anhydride copolymer composed of a stearic acid dimer and sebacic acid. Abs were slowly released from all the polymeric carriers during 30 days of continuous immersion in buffered saline. The ability of anti-hCG to bind antigen was retained following release from EVAc matrices. Only minor Ab aggregation was observed following release from either polymer. Polymeric delivery systems, similar to those described here, may become an important element in the delivery of mAbs to humans for immunoprotection against infectious diseases or the delivery of mAb-conjugates for immunotherapy against cancer.

Anhydrides↗
PubMed1992

Controlled vaginal delivery of antibodies in the mouse.

Controlled delivery of monoclonal antibodies to the mucus secretions of the vagina might provide women with passive immunoprotection against both sexually transmitted diseases and unwanted pregnancy. We have developed intravaginal devices composed of poly(ethylene-co-vinyl acetate) (EVAc) that continuously release IgG antibodies for over 30 days into buffered saline, and we have tested these devices in the vagina of mice. Polymeric devices containing either BSA (as a test reagent for proteins) or anti-hCG antibody, when inserted into the vaginas of mice, provided a continuous supply of either BSA or hCG-binding antibodies to the vaginal mucus for 30 days. Antibodies released by the devices achieved high concentration in the mucus within the lumen of the vagina, but did not significantly ascend into the uterine horns, as determined by epifluorescence microscopy of fluorescently labeled mouse IgG and by immunohistochemical localization of rabbit IgG. Our results suggest that long-term intravaginal delivery of functionally intact antibodies can be achieved with devices composed of EVAc.

Administration, Intravaginal↗