Chemokine targets in acute brain injury and disease

Genetically modified macrophages accomplish targeted gene delivery to the inflamed brain in transgenic Parkin Q311X(A) mice: importance of administration routes

Cell-based drug delivery systems have generated an increasing interest in recent years. We previously demonstrated that systemically administered macrophages deliver therapeutics to CNS, including glial cell line-derived neurotrophic factor (GDNF), and produce potent effects in Parkinson’s disease (PD) mouse models. Herein, we report fundamental changes in biodistribution and brain bioavailability of macrophage-based formulations upon different routes of administration: intravenous, intraperitoneal, or intrathecal injections. The brain accumulation of adoptively transferred macrophages was evaluated by various imaging methods in transgenic Parkin Q311(X)A mice and compared with those in healthy wild type littermates. Neuroinflammation manifested in PD mice warranted targeting macrophages to the brain for each route of administration. The maximum amount of cell-carriers in the brain, up to 8.1% ID/g, was recorded followed a single intrathecal injection. GDNF-transfected macrophages administered through intrathecal route provided significant increases of GDNF levels in different brain sub-regions, including midbrain, cerebellum, frontal cortex, and pons. No significant offsite toxicity of the cell-based formulations in mouse brain and peripheral organs was observed. Overall, intrathecal injection appeared to be the optimal administration route for genetically modified macrophages, which accomplished targeted gene delivery, and significant expression of reporter and therapeutic genes in the brain.

Macrophages with cellular backpacks for targeted drug delivery to the brain

Most potent therapeutics are unable to cross the blood-brain barrier following systemic administration, which necessitates the development of unconventional, clinically applicable drug delivery systems. With the given challenges, biologically active vehicles are crucial to accomplishing this task. We now report a new method for drug delivery that utilizes living cells as vehicles for drug carriage across the blood brain barrier. Cellular backpacks, 7-10 μm diameter polymer patches of a few hundred nanometers in thickness, are a potentially interesting approach, because they can act as drug depots that travel with the cell-carrier, without being phagocytized. Backpacks loaded with a potent antioxidant, catalase, were attached to autologous macrophages and systemically administered into mice with brain inflammation. Using inflammatory response cells enabled targeted drug transport to the inflamed brain. Furthermore, catalase-loaded backpacks demonstrated potent therapeutic effects deactivating free radicals released by activated microglia in vitro. This approach for drug carriage and release can accelerate the development of new drug formulations for all the neurodegenerative disorders.

GDNF-transfected macrophages produce potent neuroprotective effects in Parkinson's disease mouse model

The pathobiology of Parkinson's disease (PD) is associated with the loss of dopaminergic neurons in the substantia nigra pars compacta (SNpc) projecting to the striatum. Currently, there are no treatments that can halt or reverse the course of PD; only palliative therapies, such as replacement strategies for missing neurotransmitters, exist. Thus, the successful brain delivery of neurotrophic factors that promote neuronal survival and reverse the disease progression is crucial. We demonstrated earlier systemically administered autologous macrophages can deliver nanoformulated antioxidant, catalase, to the SNpc providing potent anti-inflammatory effects in PD mouse models. Here we evaluated genetically-modified macrophages for active targeted brain delivery of glial cell-line derived neurotropic factor (GDNF). To capitalize on the beneficial properties afforded by alternatively activated macrophages, transfected with GDNF-encoded pDNA cells were further differentiated toward regenerative M2 phenotype. A systemic administration of GDNF-expressing macrophages significantly ameliorated neurodegeneration and neuroinflammation in PD mice. Behavioral studies confirmed neuroprotective effects of the macrophage-based drug delivery system. One of the suggested mechanisms of therapeutic effects is the release of exosomes containing the expressed neurotropic factor followed by the efficient GDNF transfer to target neurons. Such formulations can serve as a new technology based on cell-mediated active delivery of therapeutic proteins that attenuate and reverse progression of PD, and ultimately provide hope for those patients who are already significantly disabled by the disease.

Macrophages offer a paradigm switch for CNS delivery of therapeutic proteins

AIMS

Active targeted transport of the nanoformulated redox enzyme, catalase, in macrophages attenuates oxidative stress and as such increases survival of dopaminergic neurons in animal models of Parkinson's disease. Optimization of the drug formulation is crucial for the successful delivery in living cells. We demonstrated earlier that packaging of catalase into a polyion complex micelle ('nanozyme') with a synthetic polyelectrolyte block copolymer protected the enzyme against degradation in macrophages and improved therapeutic outcomes. We now report the manufacture of nanozymes with superior structure and therapeutic indices.

METHODS

Synthesis, characterization and therapeutic efficacy of optimal cell-based nanoformulations are evaluated.

RESULTS

A formulation design for drug carriers typically works to avoid entrapment in monocytes and macrophages focusing on small-sized nanoparticles with a polyethylene glycol corona (to provide a stealth effect). By contrast, the best nanozymes for delivery in macrophages reported in this study have a relatively large size (≈ 200 nm), which resulted in improved loading capacity and release from macrophages. Furthermore, the cross-linking of nanozymes with the excess of a nonbiodegradable linker ensured their low cytotoxicity, and efficient catalase protection in cell carriers. Finally, the 'alternatively activated' macrophage phenotype (M2) utilized in these studies did not promote further inflammation in the brain, resulting in a subtle but statistically significant effect on neuronal regeneration and repair in vivo.

CONCLUSION

The optimized cross-linked nanozyme loaded into macrophages reduced neuroinflammatory responses and increased neuronal survival in mice. Importantly, the approach for nanoformulation design for cell-mediated delivery is different from the common requirements for injectable formulations.

Polyelectrolyte complex optimization for macrophage delivery of redox enzyme nanoparticles

BACKGROUND

We posit that cell-mediated drug delivery can improve transport of therapeutic enzymes to the brain and decrease inflammation and neurodegeneration seen during Parkinson's disease. Our prior works demonstrated that macrophages loaded with nanoformulated catalase ('nanozyme') then parenterally injected protect the nigrostriatum in a murine model of Parkinson's disease. Packaging of catalase into block ionomer complex with a synthetic polyelectrolyte block copolymer precludes enzyme degradation in macrophages.

METHODS

We examined relationships between the composition and structure of block ionomer complexes with a range of block copolymers, their physicochemical characteristics, and loading, release and catalase enzymatic activity in bone marrow-derived macrophages.

RESULTS

Formation of block ionomer complexes resulted in improved aggregation stability. Block ionomer complexes with ε-polylysine and poly(L-glutamic acid)-poly(ethylene glycol) demonstrated the least cytotoxicity and high loading and release rates. However, these formulations did not efficiently protect catalase inside macrophages.

CONCLUSION

Nanozymes with polyethyleneimine- and poly(L-lysine)(10)-poly(ethylene glycol) provided the best protection of enzymatic activity for cell-mediated drug delivery.

Cell-mediated drug delivery

INTRODUCTION

Drug targeting to sites of tissue injury, tumor or infection with limited toxicity is the goal for successful pharmaceutics. Immunocytes (including mononuclear phagocytes (dendritic cells, monocytes and macrophages), neutrophils and lymphocytes) are highly mobile; they can migrate across impermeable barriers and release their drug cargo at sites of infection or tissue injury. Thus, immune cells can be exploited as Trojan horses for drug delivery.

AREAS COVERED

This paper reviews how immunocytes laden with drugs can cross the blood-brain or blood-tumor barriers to facilitate treatments for infectious diseases, injury, cancer, or inflammatory diseases. The promises and perils of cell-mediated drug delivery are reviewed, with examples of how immunocytes can be harnessed to improve therapeutic end points.

EXPERT OPINION

Using cells as delivery vehicles enables targeted drug transport and prolonged circulation times, along with reductions in cell and tissue toxicities. Such systems for drug carriage and targeted release represent a new disease-combating strategy being applied to a spectrum of human disorders. The design of nanocarriers for cell-mediated drug delivery may differ from those used for conventional drug delivery systems; nevertheless, engaging different defense mechanisms in drug delivery may open new perspectives for the active delivery of drugs.

Active Targeted Macrophage-mediated Delivery of Catalase to Affected Brain Regions in Models of Parkinson's Disease

We previously demonstrated that monocyte-macrophage based drug delivery can be applied to a spectrum of infectious, neoplastic, and degenerative disorders. In particular, bone marrow-derived macrophages (BMM) loaded with nano formulated catalase, "nanozyme", were shown to attenuate neuro inflammation and nigrostriatal degeneration in rodent models of Parkinson's disease (PD). Nonetheless, the pharmacokinetics and biodistribution of BMM-incorporated nanozyme has not been explored. To this end, we now demonstrate that BMM, serving as a "depot" for nanozyme, increased area under the curve(AUC), half-life, and mean residence time in blood circulation of the protein when compared to the nanozyme administered alone. Accordingly, bioavailability of the nanozyme for the brain, spleen, kidney, and liver was substantially increased. Importantly, nanozyme-loaded BMM targeted diseased sites and improved transport across the blood brain barrier. This was seen specifically in affected brain subregions in models of PD. Engaging natural immune cells such as monocyte-macrophages as drug carriers provides a new perspective for therapeutic delivery for PD and also likely a range of other inflammatory and degenerative diseases.

Scavenging roles of chemokine receptors: chemokine receptor deficiency is associated with increased levels of ligand in circulation and tissues

In vitro studies have implicated chemokine receptors in consumption and clearance of specific ligands. We studied the role that various signaling chemokine receptors play during ligand homeostasis in vivo. We examined the levels of ligands in serum and CNS tissue in mice lacking chemokine receptors. Compared with receptor-sufficient controls, Cx3cr1(-/-) mice exhibited augmented levels of CX3CL1 both in serum and brain, and circulating levels of CXCL1 and CXCL2 were increased in Cxcr2(-/-) mice. CCR2-deficient mice showed significantly increased amounts of circulating CCL2 compared with wild-type mice. Cxcr3(-/-) mice revealed increased levels of circulating and brain CXCL10 after experimental autoimmune encephalomyelitis (EAE) induction. CCR2-deficient peripheral blood and resident peritoneal cells exhibited reduced binding capacity and biologic responses to the CCR1 ligand CCL3, suggesting that elevated levels of CCR2 ligands had down-regulated CCR1. The results indicate that signaling chemokine receptors clear chemokines from circulation and tissues. These homeostatic functions of signaling chemokine receptors need to be integrated into safety and efficacy calculations when considering therapeutic receptor blockade.

A macrophage-nanozyme delivery system for Parkinson's disease

Selective delivery of antioxidants to the substantia nigra pars compacta (SNpc) during Parkinson's disease (PD) can potentially attenuate oxidative stress and as such increase survival of dopaminergic neurons. To this end, we developed a bone-marrow-derived macrophage (BMM) system to deliver catalase to PD-affected brain regions in an animal model of human disease. To preclude BMM-mediated enzyme degradation, catalase was packaged into a block ionomer complex with a cationic block copolymer, polyethyleneimine-poly(ethylene glycol) (PEI-PEG). The self-assembled catalase/PEI-PEG complexes, "nanozymes", were ca. 60 to 100 nm in size, stable in pH and ionic strength, and retained antioxidant activities. Cytotoxicity was negligible over a range of physiologic nanozyme concentrations. Nanozyme particles were rapidly, 40-60 min, taken up by BMM, retained catalytic activity, and released in active form for greater than 24 h. In contrast, "naked" catalase was rapidly degraded. The released enzyme decomposed microglial hydrogen peroxide following nitrated alpha-synuclein or tumor necrosis factor alpha activation. Following adoptive transfer of nanozyme-loaded BMM to 1-methyl 4-phenyl 1,2,3,6-tetrahydropyridine-intoxicated mice, ca. 0.6% of the injected dose were found in brain. We conclude that cell-mediated delivery of nanozymes can reduce oxidative stress in laboratory and animal models of PD.

The chemokine fractalkine in patients with severe traumatic brain injury and a mouse model of closed head injury

The potential role of the chemokine Fractalkine (CX3CL1) in the pathophysiology of traumatic brain injury (TBI) was investigated in patients with head trauma and in mice after experimental cortical contusion. In control individuals, soluble (s)Fractalkine was present at low concentrations in cerebrospinal fluid (CSF) (12.6 to 57.3 pg/mL) but at much higher levels in serum (21,288 to 74,548 pg/mL). Elevation of sFractalkine in CSF of TBI patients was observed during the whole study period (means: 29.92 to 535.33 pg/mL), whereas serum levels remained within normal ranges (means: 3,100 to 59,159 pg/mL). Based on these differences, a possible passage of sFractalkine from blood to CSF was supported by the strong correlation between blood-brain barrier dysfunction (according to the CSF-/serum-albumin quotient) and sFractalkine concentrations in CSF (R = 0.706; P < 0.01). In the brain of mice subjected to closed head injury, neither Fractalkine protein nor mRNA were found to be augmented; however, Fractalkine receptor (CX3CR1) mRNA steadily increased peaking at 1 week postinjury (P < 0.05, one-way analysis of variance). This possibly implies the receptor to be the key factor determining the action of constitutively expressed Fractalkine. Altogether, these data suggest that the Fractalkine-CX3CR1 protein system may be involved in the inflammatory response to TBI, particularly for the accumulation of leukocytes in the injured parenchyma.

Injury‐induced NF‐κB activation in the hippocampus: implications for neuronal survival

Nuclear factor (NF)-kappaB p50 protein is involved in promoting survival in hippocampal neurons after trimethyltin (TMT)-injury. In the current study, hippocampal NF-kappaB activity was examined and quantitated from transgenic kappaB-lacZ reporter mice after chemical-induced injury. NF-kappaB activity was localized primarily to hippocampal neurons and significantly elevated over that in saline-treated mice between 4 and 21 days after TMT injection. Seven days after TMT injection, a timepoint of elevated NF-kappaB activity, gene expression in the hippocampus was studied by microarray analysis through comparison of expression profiles between treated nontransgenic and p50-null mice with their saline-injected controls. Seventeen genes increased in nontransgenic TMT-treated mice relative to saline-treated as well as showing no increase in p50-null mice, indicating a role for p50 in their regulation. One of these genes, the Na+, K+-ATPase-gamma subunit, was detected in brain for the first time. Several of the genes modulated by NF-kappaB are potentially related to neuroplasticity, providing additional evidence that this transcription factor is a neuroprotective signal in the hippocampus.

A potential role for CXCR3 chemokines in the response to ocular HSV infection

Corneal infection with herpes simplex virus (HSV) leads to the recruitment of immune cells to the eye itself, the trigeminal ganglion and the brainstem. In addition, some resident cells in these target tissues are infected by HSV, activated during the inflammatory response or both. Chemokine signaling is an important component of the regulatory circuit governing the host immune response to virus infection. This review discusses chemokine responses in relation to HSV infection of the cornea emphasizing the role of CXCR3 chemokine signaling by the IFN-gamma inducible ligands MIG, IP10 and I-TAC and includes discussion of their potential role in immunopathology in the nervous system.

CXC-chemokines KC and macrophage inflammatory protein-2 (MIP-2) synergistically induce leukocyte recruitment to the central nervous system in rats

Intracisternal injection of the CXC-chemokines KC or macrophage inflammatory protein (MIP)-2 induced a pleocytosis in the cerebrospinal fluid (CSF) of rats in a dose dependent way. MIP-2 was much more potent than KC. The concurrent injection of both chemokines revealed a profound synergistic effect on leukocyte recruitment into CSF.

Neuropathological imaging: in vivo detection of glial activation as a measure of disease and adaptive change in the brain

Glial cells form a structural and functional network with complex cell-cell communication pathways that enable fast and slow signalling amongst themselves as well as with neurons. They exert regulatory influence on normal synaptic transmission and alter it in disease. It is becoming increasingly clear that an understanding of brain function in disease conditions requires a better account of the highly plastic, disease-associated changes in glial physiology in vivo. Particularly, microglia, the brain's ubiquitous but normally inconspicuous immune effector cell, are prominently involved in many brain diseases. They respond rapidly and in a territorially highly confined way to subtle, acute and chronic pathological stimuli. Detection of microglial activation provides diagnostically useful formal parameters of disease, such as the accurate spatial localisation, disease progression and the secondary neurodegenerative or adaptive changes remote from the primary site of disease. The latter has potential relevance for the understanding of disease-induced brain plasticity. Systematic attempts are now undertaken, using positron emission tomography and a ligand with relative selectivity for activated microglia, to develop generic imaging tools for a cellular in vivo neuropathology.

Response of chemokine antagonists to inflammation in injured spinal cord

Inflammation is a primary reaction to infection, allergic disorders, autoimmune diseases, and mechanical injury. The goal of an inflammatory response is to rapidly respond to noxious stimuli, such as trauma or pathogen, with a controlled amplification of cellular activation to eliminate, control, or wall off the triggering agent. Although the inflammatory response is necessary for resolution of the pathogenic event, by stander or collateral tissue damage is caused by the toxic nature of many of its by-products. It is characterized by the infiltration of leukocytes into the affected area. Chemokines and their receptors play an essential role as mediators of leukocyte infiltration. In most cases this response is so vigorous that its control, especially in the central nervous system, would inhibit recovery. The benefits of anti-inflammatory therapy based on interference with the chemokine system has been established in animal models and is being pursued with chemokine antibodies and receptor antagonists. Prolonged treatment with a broad-spectrum chemokine antagonist, vMIPII, has been shown to reduce the rate of infiltration of monocytes into injured rat spinal cord and promote survival.

Functional expression of CCR2 by human fetal astrocytes

Astrocytes from different sources bind the chemokine monocyte chemoattractant factor (MCP-1), yet functional expression in these cells of CCR2, the major receptor for this ligand, has been a matter of controversy. Here we show that cultured human fetal astrocytes express CCR2 at the mRNA and protein levels, and display chemotaxis and calcium flux in response to MCP-1. Surface CCR2 protein expression and MCP-1 binding activity were observed to undergo near parallel downmodulation and recovery following MCP-1 exposure, supporting the argument that CCR2, and not another receptor, mediates MCP-1 ligation in these cells. Downmodulation was further determined to occur via receptor internalization, and to apparently proceed via both clathrin-coated vesicles and caveolae, the latter being a novel mode for the endocytosis of chemokine receptors. Insofar as MCP-1 is thought to mediate inflammatory and developmental processes within the central nervous system (CNS), such astrocyte responses to this chemokine are likely to significantly impact physiological and pathophysiological events at the blood-brain barrier and within the CNS parenchyma.