Release Depot Research Articles

Synthesis and characterization of β-cyclodextrin-conjugated alginate hydrogel for controlled release of hydrocortisone acetate in response to mechanical stimulation

Alginate hydrogels are a class of biomaterials that can be used as local release depots for therapeutic agents. A particular drug that can take advantage of alginate hydrogel for controlled release is hydrocortisone acetate. Hydrocortisone acetate is a widely used anti-inflammatory agent, but is limited in application due to poor solubility and lack of controlled delivery. To overcome this limitation, a mechanically responsive β-cyclodextrin-conjugated alginate (Alg-β-CD) hydrogel was synthesized and characterized for enhanced aqueous solubility and controlled release of hydrocortisone acetate. We demonstrated that mono-6-deoxy-6-ethylenediamine-β-cyclodextrin and hydrocortisone acetate formed a 1:1 inclusion complex, thus resulting in marked increase in hydrocortisone acetate solubility, while causing no significant inhibition to the growth of cultured mouse fibroblasts (L929). More importantly, the release of hydrocortisone acetate from the hydrogel system was increasingly sensitive to mechanical compression, and the mechanical responsiveness of hydrocortisone acetate release increased dramatically as the concentration of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin increased from 0% to 46%, whereas the swelling rate and stiffness of the hydrogel decreased as the concentration of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin increased. The mechanical responsiveness of hydrocortisone acetate release was attributable to conformational distortion of mono-6-deoxy-6-ethylenediamine-β-cyclodextrin moieties and deformation of the polymer network. Moreover, we demonstrated that the hydrogel continuously released and accumulated hydrocortisone acetate in the medium when compressed for up to 72 h, which led to increasing suppression of nitric oxide production in the lipopolysaccharide-stimulated mouse macrophages (RAW264.7), indicating desirable anti-inflammatory effect at the cell level. Hence, this hydrogel system may provide a useful platform for drug delivery, such as hydrocortisone acetate release to wound site, by intentionally generated mechanical force.

Rational design of block copolymer micelles to control burst drug release at a nanoscale dimension

To circumvent the problem of burst drug release from polymeric micelles, we designed three layered ABC micelles consisting of methoxy poly(ethylene oxide) (PEO) as the shell layer (A block); poly(lactic acid) (PLA) of different stereo-chemistries as the outer core (B block) and poly(α-benzylcarboxylate-ε-caprolactone) (PBCL) or poly(ε-caprolactone) (PCL) as the inner core (C block). The micelles were used to encapsulate a model hydrophobic drug, nimodipine. The effect of PLA (B block) incorporation and stereochemistry on the formation of semi crystalline outer cores in ABC triblock copolymer micelles, micelle stability, drug loading and release was then assessed in comparison to diblock copolymer micelles. The PLA outer core was expected to act as a barrier lowering the rate of drug diffusion out of the micellar carrier owing to a high Flory Huggins interaction parameter between nimodipine and PLA (χ=1.35). Introduction of PLA outer cores in ABC block copolymer micelles reduced the burst release of nimodipine from polymeric micelles without jeopardizing its high encapsulation efficiency. In ABC polymeric micelles with stereo-regular PLA blocks; semi-crystalline outer PLA cores were not formed, which was in contrast to PEO–PLA diblock copolymer micelles. Accordingly, PLA stereo-chemistry had no significant effect on drug release in ABC polymeric micelles. In contrast to diblock copolymers, no sign of stereo-complexation in mixed micelles composed of a 50:50 mixture of PdLA and PlLA containing ABC triblock copolymers was observed. The results showed the capability of properly designed ABC triblock copolymer micelles as reservoirs for drug solubilization and depot release at nanoscale dimensions. Statement of SignificancePolymeric micelles are core–shell nanostructures that are widely used for drug delivery. Their hydrophobic core accommodates poor water soluble drugs and their hydrophilic shell allows the whole structure to be water soluble. A common problem with the use of polymeric micelles is leakage of the incorporated drug from these carriers. Here we have shown that a properly designed three layered (ABC) block copolymer micelle with drug compatible blocks at the inner core and drug incompatible blocks at the outer core can be used to reduce the initial fast rate of drug release while providing high amount of drug encapsulated in the core. Moreover, changes in the chemical structure of the inner core may be used to modify the stability of these systems.

A modified emulsion gelation technique to improve buoyancy of hydrogel tablets for floating drug delivery systems

The use of buoyant or floating hydrogel tablets is of particular interest in the sustained release of drugs to the stomach. They have an ability to slow the release rates of drugs by prolonging their absorption window in the upper part of the gastrointestinal (GI) tract. In this study we synthesized bioactive hydrogels that have sustainable release rates for drugs in the stomach based on a hydrogel preparation technique that employs emulsifying surfactants. The emulsion gelation technique, which encapsulates oil droplets within the hydrogels during crosslinking, was used to decrease their specific gravity in aqueous environments, resulting in floating drug release depots. Properties such as swelling, buoyancy, density and drug release were manipulated by changing the polymer concentrations, surfactant percentages and the oil:polymer ratios. The relationship between these properties and the hydrogel's floating lag time was documented. The potential for this material to be used as a floating drug delivery system was demonstrated.

Thermosensitive hydrogel drug delivery system containing doxorubicin loaded CS–GO nanocarriers for controlled release drug in situ

Local delivery of antitumour drugs provided a high local concentration, the intention of increased antitumour and decreased systemic therapy. An injectable thermosensitive hydrogel is commonly used as a local drug delivery system (DDS). In this paper, a novel local hydrophilic doxorubicin (DOX) DDS, chitosan functionalised graphene oxide (CS–GO) nanocarriers in polylactide (PLA)–poly(ethylene glycol) (PEG)–PLA thermosensitive hydrogel, was demonstrated. The DOX loaded CS–GO nanocarriers (DOX/CS–GO) were prepared via π–π stacking and hydrophobic interactions, which presented a superior loading capacity for DOX, and then DOX/CS–GO were incorporated into the thermosensitive hydrous matrix. The obtained injectable hydrophilic DOX delivery system was flowing sol at ambient temperature but became non-flowing gel at body temperature and can act as a depot for sustained release of DOX in situ. The in vitro cytotoxicity test showed that the PLA–PEG–PLA hydrogel and CS–GO nanocarriers were non-cytotoxic. The obtained CS–GO/DOX nanocarriers not only showed increased cellular uptake but also enhanced cytotoxicity. The in vitro release of PLA–PEG–PLA/(CS–GO/DOX) complexes was sustained for >200 h. These results suggested that this injectable composite hydrogel is a potential candidate as drug carrier and in clinical applications in situ.

Regioselective Ring-Opening Polymerization of a Polyhydroxycarboxylic Acid for the Synthesis of a Nanoscale Carrier Material with pH-Dependent Stability and Sustained Drug Release.

Synthetic polyesters are usually composed of monohydroxycarboxylic acids to avoid the problem of regioselectivity during ring-opening polymerization. In contrast, the linear polyester BICpoly contains four secondary OH groups and is nevertheless esterified regioselectively at only one of these positions. Neither the synthesis of the tricyclic monomers nor the ring-opening polymerization requires protecting groups, making BICpoly an attractive novel and biocompatible polymer. BICpoly nanoparticles can be loaded with low-molecular weight drugs or coated onto surfaces as thin films. The release of loaded compounds makes BICpoly an attractive depot for drug release, as shown herein by loading BICpoly with dyes or the cytostatic drug doxorubicin. BICpoly is distinguishable from other polymers by its characteristic pH-dependent degradation.

Polymeric nanoparticles for co-delivery of synthetic long peptide antigen and poly IC as therapeutic cancer vaccine formulation

The aim of the current study was to develop a cancer vaccine formulation for treatment of human papillomavirus (HPV)-induced malignancies. Synthetic long peptides (SLPs) derived from HPV16 E6 and E7 oncoproteins have been used for therapeutic vaccination in clinical trials with promising results. In preclinical and clinical studies adjuvants based on mineral oils (such as incomplete Freund's adjuvant (IFA) and Montanide) are used to create a sustained release depot at the injection site. While the depot effect of mineral oils is important for induction of robust immune responses, their administration is accompanied with severe adverse and long lasting side effects. In order to develop an alternative for IFA family of adjuvants, polymeric nanoparticles (NPs) based on hydrophilic polyester (poly(d,l lactic-co-hydroxymethyl glycolic acid) (pLHMGA)) were prepared. These NPs were loaded with a synthetic long peptide (SLP) derived from HPV16 E7 oncoprotein and a toll like receptor 3 (TLR3) ligand (poly IC) by double emulsion solvent evaporation technique. The therapeutic efficacy of the nanoparticulate formulations was compared to that of HPV SLP+poly IC formulated in IFA. Encapsulation of HPV SLP antigen in NPs substantially enhanced the population of HPV-specific CD8+ T cells when combined with poly IC either co-encapsulated with the antigen or in its soluble form. The therapeutic efficacy of NPs containing poly IC in tumor eradication was equivalent to that of the IFA formulation. Importantly, administration of pLHMGA nanoparticles was not associated with adverse effects and therefore these biodegradable nanoparticles are excellent substitutes for IFA in cancer vaccines.

Preparation of an injectable depot system for long-term delivery of alendronate and evaluation of its anti-osteoporotic effect in an ovariectomized rat model

We prepared an injectable depot system for the long-term delivery of alendronate using a solid/water/oil/water multiple emulsion technique with poly(lactic-co-glycolic acid) as a carrier. The microparticles were spherical with smooth surfaces, ranging from 20 to 70μm in size. The microspheres (ALD-HA-RG504H-MC70) were optimally prepared by introducing a viscous material (hyaluronic acid) and a co-solvent system in the inner aqueous and oil phases, respectively, and showed a significantly increased drug encapsulation efficacy (>70%); the initial burst release was <10% after 1 day. In vitro drug release from ALD-HA-RG504H-MC70 followed zero-order kinetics for approximately 4 weeks and the alendronate plasma level was maintained for more than 1 month after intramuscular injection in rabbits. The ovariectomized (OVX) rats with ALD-HA-RG504H-MC70 injected intramuscularly (0.9mg alendronate/kg/4 weeks) had 112% and 482% increased bone mineral density and trabecular area in the tibia than the OVX controls, respectively, and showed significant improvements in trabecular microarchitecture and bone strength. Furthermore, the major biomarkers of bone turnover revealed that ALD-HA-RG504H-MC70 suppressed effectively the progression of osteoporosis and facilitated new bone formation. Therefore, this sustained release depot system may improve patient compliance and therapeutic efficacy by reducing dose amounts and frequency with minimal adverse reactions.

Formulation of in situ chemically cross-linked hydrogel depots for protein release: from the blob model perspective.

The fast release rate and the undesirable covalent binding are two major problems often encountered in formulating in situ chemically cross-linked hydrogel as protein release depot, particularly when prolonged release over months is desirable. In this study, we applied the De Gennes' blob theory to analyze and tackle these two problems using a vinylsulfone-thiol (VS-SH) reaction based in situ hydrogel system. We showed that the simple scaling relation ξb ≈ Rg(c/c*)(-v/(3v-1)) is applicable to the in situ hydrogel and the mesh size estimated from the precursor polymer parameters is a reasonable match to experimental results. On the other hand, as predicted by the theory and confirmed by experiments, the drug diffusion within hydrogel depends mainly on polymer concentration but not the degree of modification (DM). The covalent binding was found to be caused by the mismatch of location between the reactive groups and the entanglement points. The mismatch and, thus, the protein binding were minimized by increasing the DM and concentration of the SH polymer relative to the VS polymer, as predicted by theory. Using these principles, an in situ hydrogel system for the controlled release of an antiangiogenic antibody therapeutics bevacizumab for 3 months was developed.

In vitro and in vivo toxicological studies of V nerve agents: Molecular and stereoselective aspects

In vitro inhibition data of cholinesterases (ChEs) and reactivation with HI 6 are presented for separated VX and VR enantiomers with high purity (enantiomer excess >99.999%). Inhibition rate constants for (−)-VR were fourfold higher than for (−)-VX. Marked higher stereoselectivity of ChEs inhibition was observed for VR compared with VX enantiomers. Low/no reactivation was determined for respective (+)-enantiomers. Results were related to orientation of (−)- and (+)-enantiomers in ChEs active sites.In vivo in swine, absorption rate constants were practically identical for VX and VR enantiomers after percutaneous application of 3xLD50 underlining relevance of amine group and postulated equilibria shifts between charged, uncharged, open and cyclic form (skin depot). In vivo toxicokinetics of VX and VR enantiomers differed markedly after 4h. Elimination of VX was much slower compared with VR.Acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibition in vivo differed for VX and VR. In vivo spontaneous reactivation was not observed for VX-inhibited AChE while VR-inhibited AChE was much faster spontaneously reactivated than expected and AChE inhibition by VR was slower than expected. Progredient BChE inhibition was detected after VX application while VR inhibited BChE weakly. Possible explanation may be impact of the agents on hemodynamics and different metabolisms. Thus, due to increase of the V agents’ blood concentration after atropine administration (depot release) the present standard therapy should be thoroughly reconsidered.

Electrospun nanofibers-mediated on-demand drug release.

A living system has a complex and accurate regulation system with intelligent sensor-processor-effector components to enable the release of vital bioactive substances on demand at a specific site and time. Stimuli-responsive polymers mimic biological systems in a crude way where an external stimulus results in a change in conformation, solubility, or alternation of the hydrophilic/hydrophobic balance, and consequently release of a bioactive substance. Electrospinning is a straightforward and robust method to produce nanofibers with the potential to incorporate drugs in a simple, rapid, and reproducible process. This feature article emphasizes an emerging area using an electrospinning technique to generate biomimetic nanofibers as drug delivery devices that are responsive to different stimuli, such as temperature, pH, light, and electric/magnetic field for controlled release of therapeutic substances. Although at its infancy, the mimicry of these stimuli-responsive nanofibers to the function of the living systems includes both the fibrous structural feature and bio-regulation function as an on demand drug release depot. The electrospun nanofibers with extracellular matrix morphology intrinsically guide cellular drug uptake, which will be highly desired to translate the promise of drug delivery for the clinical success.

Improving clinical outcomes for naltrexone as a management of problem alcohol use.

Despite being a relatively effective and safe treatment, the clinical management of alcohol abuse/dependence by oral naltrexone can be compromised due to the patient's non-compliance with daily use of this medication. Over the past decade an increasing body of research has suggested that the use of sustained release depot naltrexone preparations can overcome this issue and deliver improved clinical outcomes. However, at the same time, research findings from diverse areas of pharmacogenetics, neurobiology and behavioural psychology have also been converging to identify variables including genetic markers, patient psychosocial characteristics and drug use history differences, or clusters of these variables that play a major role in mediating the response of alcohol abuse/dependent persons to treatment by naltrexone. While this article does not attempt to review all available data pertaining to an individual alcohol dependent patient's response to treatment by naltrexone, it does identify relevant research areas and highlights the importance of data arising from them. The characterization of clinical markers, to identify those patients who are most likely to benefit from naltrexone and to tailor a more individual naltrexone treatment, will ultimately provide significant benefit to both patients and clinicians by optimizing treatment outcome.

Abstract 449: Progesterone-induced immunosuppression thwarts immunosurveillance to tumors and promotes lung metastasis in a breast cancer model.

Abstract Exposure to sexual hormones is one of the strongest risk factors for breast cancer. Increased risk is entwined with a greater number of reproductive cycles and the use of progestin-containing hormone replacement therapy. In addition, the importance of progesterone in dampening immune response was illustrated in several models of infection and pregnancy. Based on the tolerogenic properties of progesterone (Pg) and its promoting role in breast cancer, in this work we investigated whether progesterone may thwart immunosurveillance and promote tumor metastasis by fostering an immunosuppressive microenvironment in breast cancer. Exogenously added Pg: (10−8M) or its synthetic analogue medroxiprogesterone acetate (MPA: 10−8M) induced the expression of the immunosuppressive protein galectin-1 (Gal1) in the hormone-dependent human breast cancer cell lines T47D and MCF-7 and in the mouse mammary adenocarcinoma C4HD. This effect was abrogated by pre-treatment with RU486 (10−7M) indicating that the progesterone receptor (PR) was involved. Interestingly, in vitro MPA treatment of human PBMC or mouse splenocytes controlled the expansion of regulatory T cells (Tregs) (CD4+CD25+Foxp3+) and skewed the balance toward a Th2-type cytokine profile. Furthermore, differentiation from naive T-cells to Tregs cells was enhanced in the presence of MPA, IL-2 and suboptimal concentrations of TGF-β. In addition, in vivo treatment with MPA (15mg 30-day release depot) of C4HD tumor-bearing mice increased both the expression of Gal1 and the frequency of Treg cells in tumor-draining lymph nodes and the tumor microenvironment. While the increase in Treg cell frequency was associated with an effect on Treg cell SMAD4 expression that potentiates TGF-β signalling, homing of Treg cells to tumor sites was supported through the induction of tumor-derived CCL22. Finally, we used a PR negative breast tumor model (4T1) to evaluate the effect of MPA on the tumor microenvironment and the consequences of this effect on tumor progression. In vivo treatment with MPA promoted lung metastasis by inducing an invasive phenotype in breast cancer cells. Co-culture of Treg cells differentiated in vivo in the presence of MPA with 4T1 cells promoted its invasive activity and modulate several genes associated with EMT, including SNAIL. In summary, these results demonstrate that progesterone hierarchically fosters an immunosuppressive tumor microenvironment that promotes metastasis by co-ordinately regulating Gal1 expression, stimulating the TGF-β pathway and augmenting the frequency of Treg cells. Our findings provide new insights into the role of progesterone in breast cancer as a crucial promoter of tumor-immune escape. Citation Format: Mariana Salatino, Tomás Dalotto, Diego O. Croci, Santiago P. Mendez Huergo, Sebastian L. Dergan Dylon, Juan P. Cerliani, Marta A. Toscano, Gabriel A. Rabinovich. Progesterone-induced immunosuppression thwarts immunosurveillance to tumors and promotes lung metastasis in a breast cancer model. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 449. doi:10.1158/1538-7445.AM2013-449

Prostate carcinoma cell growth-inhibiting hydrogel supports axonal regeneration in vitro

Prostate cancer is the most common malignant tumor in men. Radical prostatectomy, the most common surgical therapy, is typically accompanied by erectile dysfunction and incontinence due to severing of the axons of the plexus prostaticus. To date, no reconstructive therapy is available as the delicate network of severed nerve fibers preclude the transplantation of autologous nerves or synthetic tube implants. Here, we present an injectable hydrogel as a regenerative matrix that polymerizes in situ and thus, adapts to any given tissue topography. The two-component hydrogel was synthesized from a hydrolyzed collagen fraction and stabilized by enzymatic crosslinking with transglutaminase. Physical analysis employing osmolarity measurements and cryosectioning revealed an isotonic, microstructured network that polymerized within 2min and displayed pronounced adhesion to abdominal tissue. Cell culturing demonstrated the biocompatibility of the gel and a general permissiveness for various neuronal and non-neuronal cell types. No effect on cell adhesion, survival and proliferation of cells was observed. A chemotherapeutic drug was integrated into the hydrogel to reduce the risk of fibrosis and tumor relapse. Significantly, when the hydrogel was employed as a drug release depot in vitro, aversive fibroblast- and prostate carcinoma cell growth was inhibited, while axonal outgrowth from peripheral nervous system explants remained completely unaffected. Taken together, these results suggest that the gel's adequate viscoelastic properties and porous microstructure, combined with its tissue adhesion and neuritotrophic characteristics in the presence of a cell type-specific cytostatic, may constitute an appropriate hydrogel implant applicable to patients suffering from prostatectomy associated side effects.

Fully embeddable chitosan microneedles as a sustained release depot for intradermal vaccination

This study introduces a microneedle transdermal delivery system, composed of embeddable chitosan microneedles and a poly(l-lactide-co-d,l-lactide) (PLA) supporting array, for complete and sustained delivery of encapsulated antigens to the skin. Chitosan microneedles were mounted to the top of a strong PLA supporting array, providing mechanical strength to fully insert the microneedles into the skin. When inserted into rat skin in vivo, chitosan microneedles successfully separated from the supporting array and were left within the skin for sustained drug delivery without requiring a transdermal patch. The microneedle penetration depth was approximately 600 μm (i.e. the total length of the microneedle), which is beneficial for targeted delivery of antigens to antigen-presenting cells in the epidermis and dermis. To evaluate the utility of chitosan microneedles for intradermal vaccination, ovalbumin (OVA; MW = 44.3 kDa) was used as a model antigen. When the OVA-loaded microneedles were embedded in rat skin in vivo, histological examination showed that the microneedles gradually degraded and prolonged OVA exposure at the insertion sites for up to 14 days. Compared to traditional intramuscular immunization, rats immunized by a single microneedle dose of OVA showed a significantly higher OVA-specific antibody response which lasted for at least 6 weeks. These results suggest that embeddable chitosan microneedles are a promising depot for extended delivery of encapsulated antigens to provide sustained immune stimulation and improve immunogenicity.

Thermosensitive Polymeric Hydrogels As Drug Delivery Systems

Thermosensitive hydrogels are very important biomaterials used in drug delivery systems (DDSs), which gained increasing attention of researchers. Thermosensitive hydrogels have great potential in various applications, such as drug delivery, cell encapsulation, tissue engineering, and etc. Especially, injectable thermosensitive hydrogels with lower sol-gel transition temperature around physiological temperature have been extensively studied. By in vivo injection, the hydrogels formed non-flowing gel at body temperature. Upon incorporation of pharmaceutical agents, the hydrogel systems could act as sustained drug release depot in situ. Injectable thermosensitive hydrogel systems have a number of advantages, including simplicity of drug formulation, protective environment for drugs, prolonged and localized drug delivery, and ease of application. The objective of this review is to summarize fundamentals, applications, and recent advances of injectable thermosensitive hydrogel as DDSs, including chitosan and related derivatives, poly(N-isopropylacrylamide)-based (PNIPAAM) copolymers, poly(ethylene oxide)/poly(propylene oxide) (PEO/PPO) copolymers and its derivatives, and poly(ethylene glycol)/ biodegradable polyester copolymers.

Aerosolized antimicrobial agents based on degradable dextran nanoparticles loaded with silver carbene complexes.

Degradable acetalated dextran (Ac-DEX) nanoparticles were prepared and loaded with a hydrophobic silver carbene complex (SCC) by a single-emulsion process. The resulting particles were characterized for morphology and size distribution using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and dynamic light scattering (DLS). The average particle size and particle size distribution were found to be a function of the ratio of the organic phase to the surfactant containing aqueous phase with a 1:5 volume ratio of Ac-DEX CH(2)Cl(2) (organic):PBS (aqueous) being optimal for the formulation of nanoparticles with an average size of 100 ± 40 nm and a low polydispersity. The SCC loading was found to increase with an increase in the SCC quantity in the initial feed used during particle formulation up to 30% (w/w); however, the encapsulation efficiency was observed to be the best at a feed ratio of 20% (w/w). In vitro efficacy testing of the SCC loaded Ac-DEX nanoparticles demonstrated their activity against both Gram-negative and Gram-positive bacteria; the nanoparticles inhibited the growth of every bacterial species tested. As expected, a higher concentration of drug was required to inhibit bacterial growth when the drug was encapsulated within the nanoparticle formulations compared with the free drug illustrating the desired depot release. Compared with free drug, the Ac-DEX nanoparticles were much more readily suspended in an aqueous phase and subsequently aerosolized, thus providing an effective method of pulmonary drug delivery.

Reliability of Postmortem Fentanyl Concentrations in Determining the Cause of Death

Transdermal fentanyl, an opioid used for management of marked pain, also is abused and may cause death. We reviewed medical examiner reports of 92 decedents who had one or more fentanyl transdermal patches on their body and had fentanyl detected in their postmortem toxicology analysis. The manners of death included 40 accidents, 36 natural, 8 suicides, 5 therapeutic complications, and 3 undetermined deaths. Among the accidental fentanyl intoxication deaths, 32 of 37 involved substance abuse. The majority (95 %) of the 37 accidental deaths involving fentanyl were multi-drug intoxications. The substance abuse deaths had a mean fentanyl blood concentration (26.4 ng/ml or μg/L) that was over twice that of the natural group (11.8 ng/ml). Our analysis suggests a relationship between total patch dosage and mean postmortem fentanyl concentration up to the 100-μg/h dose. The very wide and overlapping ranges of postmortem fentanyl concentrations effectively nullify the utility of correlating the dose and expected postmortem concentration for any particular death. Based on the variable relationship between dose and blood concentration, the antemortem dose cannot be reliably predicted based on the postmortem concentration. This does not, however, render the medical examiner/coroner unable to determine the cause and manner of death because the toxicology results are only one datum point among several that are considered. Although there was a weakly positive relationship between body mass index and fentanyl concentration, further research is needed to determine whether adipose tissue represents a significant depot for postmortem release of fentanyl.

Biodegradable donepezil lipospheres for depot injection: optimization and in-vivo evaluation

The purpose of this study was to develop an injectable depot liposphere delivery system with high loading capacity for controlled delivery of donepezil to decrease dosing frequency and increase patient compliance. A 3(2) full factorial design was employed to study the effect of lipid type and drug-to-lipid ratio on the yield, encapsulation efficiency, mean diameter and the time required for 50% drug release (t(50%) ). The pharmacokinetic behaviour of the lipospheres in rabbits was studied using tandem mass spectrometry. The yields of preparations were in the range of 66.22-90.90%, with high encapsulation efficiencies (89.68-97.55%) and mean particle size of 20.68-35.94 µm. Both lipid type and drug-to-lipid ratio significantly affected t(50%) (P<0.0001), where the lipids can be arranged: glyceryl tripalmitate>compritol>cetyl alcohol, and the drug-to-lipid ratios can be arranged: 1:40>1:20>1:10. The flow time of lipospheres through 19-gauge syringe needle was less than 6s indicating good syringeability. The mean residence time of the subcutaneous and intramuscular lipospheres was significantly higher than the solution (almost 20 fold increase), with values of 11.04, 11.34 and 0.53 days, respectively (P<0.01). Subcutaneous and intramuscular delivery of donepezil glyceryl tripalmitate lipospheres achieves depot release, allowing less frequent dosing.

Development of a thermoresponsive chitosan gel combined with human mesenchymal stem cells and desferrioxamine as a multimodal pro-angiogenic therapeutic for the treatment of critical limb ischaemia

Critical limb ischaemia (CLI) is a debilitating ischaemic disease caused by vascular occlusion. Pro-angiogenic therapeutics have the potential to produce collateral vasculature, delaying or negating the need for amputation or invasive revascularisation. Thermoresponsive hydrogels can provide an in situ depot for the sustained release of drugs and provide protection and cohesion for encapsulated cells. Human mesenchymal stem cells (hMSCs) have demonstrated strong angiogenic potential in vitro and angiogenic efficacy in vivo. Desferrioxamine (DFO), a pharmacological activator of the pro-angiogenic hypoxia inducible factor-1α pathway, has shown pro-angiogenic efficacy in vivo. This study combined hMSCs and DFO with a thermoresponsive chitosan/β-glycerophosphate (β-GP) gel, to function as an injectable, multimodal, pro-angiogenic therapeutic for the treatment of CLI. This gel underwent a thermogelation beginning at 33°C, and provided a sustained, biologically active release of DFO over the space of seven days, whilst permitting the survival, proliferation and migration of encapsulated hMSCs. hMSCs encapsulated in gel containing a 100μM concentration of DFO displayed an upregulation in VEGF expression. The combination of hMSCs and DFO within the gel resulted in a synergistic enhancement in bioactivity, as measured by increased VEGF expression in gel-exposed human umbilical vein endothelial cells. This formulation displays significant potential as an injectable pro-angiogenic therapeutic for the treatment of CLI.

Targeted polymeric therapeutic nanoparticles: design, development and clinical translation.

Polymeric materials have been used in a range of pharmaceutical and biotechnology products for more than 40 years. These materials have evolved from their earlier use as biodegradable products such as resorbable sutures, orthopaedic implants, macroscale and microscale drug delivery systems such as microparticles and wafers used as controlled drug release depots, to multifunctional nanoparticles (NPs) capable of targeting, and controlled release of therapeutic and diagnostic agents. These newer generations of targeted and controlled release polymeric NPs are now engineered to navigate the complex in vivo environment, and incorporate functionalities for achieving target specificity, control of drug concentration and exposure kinetics at the tissue, cell, and subcellular levels. Indeed this optimization of drug pharmacology as aided by careful design of multifunctional NPs can lead to improved drug safety and efficacy, and may be complimentary to drug enhancements that are traditionally achieved by medicinal chemistry. In this regard, polymeric NPs have the potential to result in a highly differentiated new class of therapeutics, distinct from the original active drugs used in their composition, and distinct from first generation NPs that largely facilitated drug formulation. A greater flexibility in the design of drug molecules themselves may also be facilitated following their incorporation into NPs, as drug properties (solubility, metabolism, plasma binding, biodistribution, target tissue accumulation) will no longer be constrained to the same extent by drug chemical composition, but also become in-part the function of the physicochemical properties of the NP. The combination of optimally designed drugs with optimally engineered polymeric NPs opens up the possibility of improved clinical outcomes that may not be achievable with the administration of drugs in their conventional form. In this critical review, we aim to provide insights into the design and development of targeted polymeric NPs and to highlight the challenges associated with the engineering of this novel class of therapeutics, including considerations of NP design optimization, development and biophysicochemical properties. Additionally, we highlight some recent examples from the literature, which demonstrate current trends and novel concepts in both the design and utility of targeted polymeric NPs (444 references).