Magnetic Drug Targeting as New Therapeutic Option for the Treatment of Biomaterial Infections

Implant-associated infections are a challenging problem in surgery. Bacteria in biofilms are difficult to treat as they are less susceptible to antibiotics or antiseptics which require high drug concentrations at the site of infection. We present a novel strategy to concentrate high antibiotic doses systemically at the target site using newly developed antibiotic-functionalized nanoparticles directed by a magnetic drug-targeting system. The important and effective antibiotic gentamicin served as antimicrobial substance and was ionically or covalently attached to magnetic nanoparticles. Subsequently, the particles were characterized thoroughly. Anti-infective properties with regard to Staphylococcus aureus and the degree of cytotoxicity concerning human umbilical vein endothelial cells were determined. The enrichment of the magnetic nanoparticles at the surface of model tubes in circulatory experiments was investigated. We describe a promising technique for the loading of magnetic nanoparticles to treat systemic infections. Gentamicin-coated magnetic nanoparticles reduced bacterial growth even beyond pathologically relevant concentrations within 24 h. Excellent concentration independent biocompatibility was found for the nanoparticles themselves and we demonstrate that the magnetic nanoparticles can be navigated and concentrated on surfaces of model implants using a permanent magnetic field.

Synthesis, characterization and assessment of suitability of trehalose fatty acid esters as alternatives for polysorbates in protein formulation

Nonionic polyethylene glycol-derived surfactants are today's choice as surfactants in protein formulations. Different groups discovered that although surface-induced stresses are reduced by these excipients, the long-term stability of different proteins decreased due to polyethylene glycol-related induction of oxidation processes under static storage conditions. In this paper, the potential of polyoxyethylene-free surfactants for protein formulation was evaluated. Three different sugar-based surfactants, 6-O-monocaprinoyl-α,α-trehalose, 6-O-monolauroyl-α,α-trehalose and 6-O-monopalmitoyl-α,α-trehalose, were synthesized in four reaction steps. These substances lack polyethylene glycol residues and can be produced from renewable resources. The chemical and physical properties of these three surfactants were investigated and compared with polysorbate 20 and 80. 6-O-monopalmitoyl-α,α-trehalose was insoluble in water at room temperature and was hence excluded from some of the further tests. The critical micellar concentration of all surfactants is in a comparable range of approximately 0.001-0.01% (m/V). The sugar-based surfactants showed slightly higher hemolytic activity than the polysorbate references. The surfactants with shorter chain length proved to be comparable to polysorbates in regard to physicochemical properties. Finally for human growth hormone, the protein-stabilizing properties against shaking-induced stress were tested and compared to polysorbate-containing formulations. Whereas in the absence of surfactant, dramatic monomer loss and aggregate formation occurred, it was found that 100% monomer content was maintained when 0.1% (m/V) 6-O-monocaprinoyl-α,α-trehalose or 6-O-monolauroyl-α,α-trehalose was added to the formulation. Polysorbate 80 at a concentration of 0.1% (m/V) also significantly stabilized the protein. Lower amounts of surfactants result in only partial stabilization. Furthermore, adsorption of human growth hormone to the container surface is reduced in the presence of the surfactants. Thus, the new sugar-based surfactants offer a promising alternative and have potential for application in protein formulations.

Zinc gluconate in the treatment of dysgeusia--a randomized clinical trial

In the treatment of dysgeusia, the use of zinc has been frequently tried, with equivocal results. The aim of the present randomized clinical trial, which involved a sufficiently large sample, was therefore to determine the efficacy of zinc treatment. Fifty patients with idiopathic dysgeusia were carefully selected. Zinc gluconate (140 mg/day; n=26) or placebo (lactose; n=24) was randomly assigned to the patients. The patients on zinc improved in terms of gustatory function (p <0.001) and rated the dysgeusia as being less severe (p <0.05). Similarly, signs of depression in the zinc group were less severe (Beck Depression Inventory, p <0.05; mood scale, p <0.05). With the exception of the salivary calcium level, which was higher in the zinc patients (p <0.05), no other significant group differences were found. In conclusion, zinc appears to improve general gustatory function and, consequently, general mood scores in dysgeusia patients.

Collagen sponges for bone regeneration with rhBMP-2

In the US alone, approximately 500,000 patients annually undergo surgical procedures to treat bone fractures, alleviate severe back pain through spinal fusion procedures, or promote healing of non-unions. Many of these procedures involve the use of bone graft substitutes. An alternative to bone grafts are the bone morphogenetic proteins (BMPs), which have been shown to induce bone formation. For optimal effect, BMPs must be combined with an adequate matrix, which serves to prolong the residence time of the protein and, in some instances, as support for the invading osteoprogenitor cells. Several factors involved in the preparation of adequate matrices, specifically collagen sponges, were investigated in order to test the performance in a new role as an implant providing local delivery of an osteoinductive differentiation factor. Another focus of this review is the current system consisting of a combination of recombinant human BMP-2 (rhBMP-2) and an absorbable collagen sponge (ACS). The efficacy and safety of the combination has been clearly proven in both animal and human trials.

Delivery systems for BMPs: factors contributing to protein retention at an application site

BACKGROUND

Recombinant human bone morphogenetic proteins (rhBMPs) are being tested in clinical studies for their capacity to elicit bone formation. Biomaterials used in delivery systems also play a critical role in supporting the osteoinductive activity of BMPs, attributable to the controlled presentation of the BMPs to target cells. Despite extensive preclinical studies, the factors contributing to local rhBMP pharmacokinetics remain to be elucidated.

METHODS

The rhBMP pharmacokinetics were studied in a rat subcutaneous implant and in an intramuscular injection model. In situ levels of rhBMPs were quantitated with use of 125I-labeled tracers. The effects of protein structural features and the nature of the biomaterial implant were explored. Osteoinduction by biomaterial+rhBMP combinations was assessed by a semiquantitative, histology-based bone score.

RESULTS

With the use of rhBMP-2, rhBMP-4, and an N-truncated rhBMP-2, the protein isoelectric point was found critical for the initial retention of rhBMPs in an implant. Osteoinduction studies carried out in parallel indicated that rhBMPs with a higher implant retention elicited more bone formation. In the clinically used collagen+rhBMP-2 device, collagen crosslinking and sterilization were most influential in rhBMP-2 retention. To increase retention at an application site, thermoreversible polymers were engineered and shown to enhance local rhBMP-2 retention, especially by injectable delivery.

CONCLUSIONS

Two critical components of an osteoinductive device--namely, the biomaterial and the rhBMP--were shown to influence local protein pharmacokinetics and osteoinductive activity of the device. Designer biomaterials can provide an additional mechanism to modulate local protein pharmacokinetics.

CLINICAL RELEVANCE

These studies form the foundation of next-generation osteoinductive devices with improved potency at sites of desired bone regeneration and reduced side effects at other sites.

Effects of processing conditions on the rheological behavior of collagen dispersions

Biomedical collagen preparations are mainly based on liquid aqueous preparations either used directly as injectables or transferred for example into solid implants or porous devices. In all cases the viscosity of the dispersion or solution has to be controlled or adjusted by pH, temperature, collagen concentration or crosslinking. We tested these effects on the rheological and structural properties of collagen fiber dispersions focusing on oscillatory rheometry. With increasing difference between pH and pI viscosity increased and went through a maximum with less rigidity of the fibers. The dispersions acted like a predominantly permanently linked network. This character changed to only partially linked at low collagen concentration due to isolation of the individual fibers. Up to 40 degrees C, temperature is a tool suitable for adjusting viscosity without changes in the network structure. At 50 degrees C, fourier transform - infrared spectroscopy (FT-IR) spectroscopy indicated the transition of the helical into random coil structure. Renaturation of the helices was found upon cooling but atomic force microscopy (AFM) indicated severe temperature induced damages of the fibers. Crosslinking with glutaraldehyde (GTA) leads to an increase in viscosity and the effect on the network structure depends on the processing conditions.

Characterization of absorbable collagen sponges as rhBMP-2 carriers

For clinical use recombinant human bone morphogenetic protein (rhBMP-2) is soaked onto an absorbable collagen sponge (ACS) for bone regeneration. Therefore, loss of rhBMP-2 upon mechanical handling during implantation and a potential effect of the carrier on in vivo retention is of interest. The interactions between drug and carrier were looked at from the application mode and the amount of protein which can be mechanically expressed from the combination was investigated. The results indicated that rhBMP-2 binds to the collagen system. The most hydrophilic double extended homodimer showed the least binding affinity to ACS. By extending the waiting time between soaking and implantation, protein incorporation could be increased. In addition, the amount of rhBMP-2 which could be expressed was reduced by heavier ACS material and allowed for a shorter waiting period, especially at lower rhBMP-2 concentration. Crosslinking of ACS with formaldehyde led to reduced binding of rhBMP-2 to collagen either by direct hindrance of binding or reduction in swelling and number of binding sites available. Higher product pH or anion concentration enabled to increase rhBMP-2 incorporation but was limited by the potential precipitation of rhBMP-2. Despite a variety of chemical changes of ACS by ethylene oxide sterilization incorporation was not changed significantly. The in vivo release kinetics of 125I-rhBMP-2 from the collagen sponge were studied using a rat ectopic implant model. The ACS/rhBMP-2 systems tested demonstrated small, but significant differences in the in vivo retention of rhBMP-2. Consequently, it is important to have as little variability in pH, anion concentration, crosslinking and ACS mass as possible to achieve consistent or maximum binding and to avoid rhBMP-2 precipitation. Furthermore, these characteristics can be important for other in vivo applications.

Characterization of absorbable collagen sponges as recombinant human bone morphogenetic protein-2 carriers

For clinical use recombinant human bone morphogenetic protein-2 (rhBMP-2) is soaked onto an absorbable collagen sponge (ACS) for bone regeneration. Therefore, loss of rhBMP-2 upon mechanical handling during implantation and a potential effect of the carrier on in vivo retention is of interest. The interactions between drug and carrier were looked at from the application mode and the amount of protein which can be mechanically expressed from the combination was investigated. The results indicated that rhBMP-2 binds to the collagen system. The most hydrophilic double extended homodimer showed the least binding affinity to ACS. By extending the waiting time between soaking and implantation, protein incorporation could be increased. In addition, the amount of rhBMP-2 which could be expressed was reduced by heavier ACS material and allowed for a shorter waiting period, especially at lower rhBMP-2 concentration. Crosslinking of ACS with formaldehyde led to reduced binding of rhBMP-2 to collagen either by direct hindrance of binding or reduction in swelling and number of binding sites available. Higher product pH or anion concentration enabled to increase rhBMP-2 incorporation but was limited by the potential precipitation of rhBMP-2. Despite a variety of chemical changes of ACS by ethylene oxide sterilization incorporation was not changed significantly. The in vivo release kinetics of (125)I-rhBMP-2 from the collagen sponge were studied using a rat ectopic implant model. The ACS/rhBMP-2 systems tested demonstrated small but significant differences in the in vivo retention of rhBMP-2. Consequently, it is important to have as little variability in pH, anion concentration, crosslinking, and ACS mass as possible to achieve consistent or maximum binding and to avoid rhBMP-2 precipitation. Furthermore, these characteristics can be important for other in vivo applications.

Bone regeneration with recombinant human bone morphogenetic protein-2 (rhBMP-2) using absorbable collagen sponges (ACS): influence of processing on ACS characteristics and formulation

The effects of variability in three parameters (mass, cross-linking with CH2O, and EtO sterilization) of three surgically implantable absorbable collagen sponges (ACS) were studied. Sponges soaked with recombinant human bone morphogenetic protein-2 (rhBMP-2) solution were analyzed for pH, conductivity, and rhBMP-2 precipitation. A method using trinitrobenzenesulfonic acid was developed to quantify the free amino groups of the collagen sponge. With up to 240 min exposure to CH2O, the amount of free amino groups was reduced to 80%. In comparison, the denaturation temperature as determined by differential scanning calorimetry (DSC) after the sponges were soaked with phosphate-buffered saline, increased from 48 to 55 degrees C, indicating stronger interactions due to cross-linking. Subsequent sterilization with EtO caused a marked decrease in the amount of free amino groups (approximately 33% of nonsterilized controls) independent of previous CH2O treatment. However, the denaturation temperature was on average 5 degrees C lower in sterilized sponges than in nonsterilized material. In contrast to CH2O exposure, the strong reaction with EtO appeared to weaken the collagen structure. Resistance of the sponge to collagenase correlated with the degree of collagen cross-linking but was slightly reduced by sterilization. In addition, the pH of ACS soaked with water was substantially increased by sterilization. Protein precipitation was a function of pH and salt concentration but there was no effect due to collagen alone. Results indicated that ACS weight has to be limited to avoid rhBMP-2 precipitation.

rhBMP-collagen sponges as osteoinductive devices: effects of in vitro sponge characteristics and protein pI on in vivo rhBMP pharmacokinetics

Osteoinductive devices, comprised of biodegradable collagen scaffolds and recombinant human Bone Morphogenetic Proteins (rhBMPs), are being currently pursued for local bone induction. To better understand the biological performance of such devices, we have carried out a series of studies to investigate the effects of sponge properties and protein structural features on the pharmacokinetics of implanted rhBMPs. The results indicated little dependence of the rhBMP-2 pharmacokinetics on the in vitro determined sponge properties. The protein isoelectric point (pI), on the other hand, was found to significantly affect the initial implant retention of rhBMPs, but not the subsequent pharmacokinetics. A 100-fold difference in the implant-retained dose could be observed depending on the type of rhBMP implanted. We conclude that protein structural features are important variables controlling in vivo pharmacokinetics of rhBMPs, and possibly the osteoinductive potency of the devices.

Collagen--biomaterial for drug delivery

The use of collagen as a biomaterial is currently undergoing a renaissance in the tissue engineering field. The biotechnological applications focus on the aspects of cellular growth or delivery of proteins capable of stimulating cellular response. However, basic knowledge about collagen biochemistry and the processing technology in combination with understanding of the physico-chemical properties is necessary for an adequate application of collagen for carrier systems. The purpose of this review article is to summarize information available on collagen dosage forms for drug delivery as well as to impart an overview of the chemical structures and the galenical properties including detailed description of the processing steps - extraction, purification, chemical crosslinking and sterilization. The most successful and stimulating applications are shields in ophthalmology, injectable dispersions for local tumor treatment, sponges carrying antibiotics and minipellets loaded with protein drugs. However, the scientific information about manipulating release properties or mechanistic studies is not as abundant as for some synthetic polymers.

Basic thermoanalytical studies of insoluble collagen matrices

Insoluble collagen has been utilized as a base material for parenteral drug carrier systems. Information on its physicochemical properties was obtained by focussing on thermoanalytical methods. On the way from the raw material to the matrices, the acidic aqueous dispersion represents an important intermediate state. DSC and FTIR revealed its complete denaturation at 43 degrees C. Dense homogeneous collagen matrices were prepared by air-drying at 25 degrees C and became denatured at 103.5 degrees C, far above normal storage temperatures. Dielectrical Thermal Analysis demonstrated transitions in the dielectrical storage and loss moduli, reflecting the dissipation of electrical energy and increased molecular mobility caused by collapse of the triple helical structure. Cross-linking of the collagen dispersion with glutaraldehyde induced no alteration in the thermoanalytical properties of dry matrices. However, in the swollen state, after incubation of the devices in phosphate buffer the transition temperature increased from 50 to 70 degrees C as cross-linking was intensified. This indicated stronger interactions between the collagen fibre structures. Dissolution tests with cytochrome c-loaded matrices showed that higher amounts of the model protein were trapped inside the matrices as more glutaraldehyde was added.

Insoluble collagen matrices for prolonged delivery of proteins

The purpose of this investigation was to evaluate the application of high molecular weight, insoluble collagen as a carrier material for proteins. Matrices were formulated and their behavior in buffer solution was investigated with focus on swelling and inner structure. Cross-linking with glutaraldehyde was introduced prior to the formation of the devices and its influence characterized. In addition, the enzymatic degradation process was studied and release experiments with systems loaded with fluorescent-labeled bovine serum albumin were carried out. Insoluble collagen matrices were characterized by intensive swelling in buffer resulting in development of a coarse porous character. Cross-linking strongly reduced the water penetration, leading to denser structures of the swollen devices. The continuous enzymatic degradation of the disk-shaped matrices by collagenase followed the kinetics of an heterogeneous enzymatic process with hindrance of proteolysis by the addition of glutaraldehyde. Release studies demonstrated that large amounts of model protein were held in the matrices with increased cross-linking degree. In presence of collagenase a prolonged release of the trapped protein over several days by matrix cleavage could be achieved. Insoluble collagen can be effective as a carrier material for proteins with an in vitro release characteristic by both diffusion-controlled and enzymatic degradation mechanisms. Cross-linking at the stage of preparing the aqueous dispersion offers an alternative to subsequent cross-linking processes.

[Hemolytic activity of tensides--determination of the interaction between O/W- and W/O-surfactants]

Using an newly-developed haemolysis method it is possible to determine quantitatively a KLH-surfactant 3000 that exists unbound in the aqueous phase of a tertiary system containing W/O-surfactants. The method depends on membrane damage of erythrocytes and is therefore a measure of the skin acceptability of a sample. The selective analysis technique works without previous preparation of complex mixtures that could lead to errors. It gives decisive evidence that KLH-surfactant 3000 that is fixed to either the W/O-surfactants or the lipid/water interface causes no membrane damage compared with free coconut/fatty acid. Haemolysis studies show that the fraction of KLH-surfactant 3000 dissolved in the aqueous phase decreases strongly with increasing amount of cetylstearyl-alcohol (CSA) up to a ratio of fatty alcohol/KLH-surfactant of approx. 0.3:5. In this range the fatty alcohol binds ten times as much O/W-surfactant in the mixed surfactant system. Further addition of CSA above the ratio 0.3:5 cause relatively little additional fixation of coconut/fatty acid, and the co-surfactant crystallises out. The rate of binding of a 1:1 mixture of CSA and glycerolmonostearate (GMS) is comparable with that of pure fatty alcohol. This mixtures also shows reduced tendency to crystallisation.