The challenge of recruitment for neurotherapeutic clinical trials in spinal cord injury.

Study Design: Narrative review by individuals experienced in the recruitment of participants to neurotherapeutic clinical trials in spinal cord injury (SCI).

Objectives: To identify key problems of recruitment and explore potential approaches to overcoming them.

Methods: Published quantitative experience with recruitment of large-scale, experimental neurotherapeutic clinical studies targeting central nervous system and using primary outcome assessments validated for SCI over the last 3 decades was summarized.

Focal expression of adeno-associated viral-mutant tau induces widespread impairment in an APP mouse model.

Adeno-associated virus serotype 6 (AAV6) viral vectors encoding mutant and normal tau were used to produce focal tau pathology. Two mutant forms of tau were used; the P301S tau mutation is associated with neurofibrillary tangle formation in humans, and the 3PO mutation leads to rapid tau aggregation and is associated with pathogenic phosphorylation and cytotoxicity in vitro. We show that adeno-associated viral injection into entorhinal cortex of normal and tau knockout animals leads to local overexpression of tau, and the presence of human tau in axons projecting to and emanating from the entorhinal cortex.

Defeating inhibition of regeneration by scar and myelin components.

Axon regeneration and the sprouting processes that underlie plasticity are blocked by inhibitory factors in the central nervous system (CNS) environment, several of which are upregulated after injury. The major inhibitory molecules are those associated with myelin and those associated with the glial scar. In myelin, NogoA, MAG, and OMgp are present on normal oligodendrocytes and on myelin debris.

Chondroitinase combined with rehabilitation promotes recovery of forelimb function in rats with chronic spinal cord injury.

Chondroitinase ABC (ChABC) in combination with rehabilitation has been shown to promote functional recovery in acute spinal cord injury. For clinical use, the optimal treatment window is concurrent with the beginning of rehabilitation, usually 2-4 weeks after injury. We show that ChABC is effective when given 4 weeks after injury combined with rehabilitation.

Cell-based therapies for Parkinson's disease.

Parkinson's disease (PD) is the second most common neurodegenerative disease worldwide, classically characterized by a triad of motor features: bradykinesia, rigidity and resting tremor. Neurodegeneration in PD critically involves the dopaminergic neurons of the substantia nigra pars compacta, which results in a severe reduction in dopamine levels in the dorsal striatum. However, the disease also exhibits extensive non-nigral pathology and as many non-motor as motor features.

In vitro modeling of perineuronal nets: hyaluronan synthase and link protein are necessary for their formation and integrity.

We have previously shown that all perineuronal nets (PNNs) bearing neurons express a hyaluronan synthase (HAS), a link protein (usually cartilage link protein-1; Crtl1) and a chondroitin sulfate proteoglycan (usually aggrecan). Animal lacking Crtl1 in the CNS lacks normal PNNs. PNNs are implicated in the control of neuronal plasticity, and interventions to modulate PNN formation will be useful for manipulating plasticity.

Animals lacking link protein have attenuated perineuronal nets and persistent plasticity.

Chondroitin sulphate proteoglycans in the extracellular matrix restrict plasticity in the adult central nervous system and their digestion with chondroitinase reactivates plasticity. However the structures in the extracellular matrix that restrict plasticity are unknown. There are many changes in the extracellular matrix as critical periods for plasticity close, including changes in chondroitin sulphate proteoglycan core protein levels, changes in glycosaminoglycan sulphation and the appearance of dense chondroitin sulphate proteoglycan-containing perineuronal nets around many neurons.

Schwann cell migration is integrin-dependent and inhibited by astrocyte-produced aggrecan.

Schwann cells transplantation has considerable promise in spinal cord trauma to bridge the site of injury and for remyelination in demyelinating conditions. They support axonal regeneration and sprouting by secreting growth factors and providing a permissive surface and matrix molecules while shielding axons from the inhibitory environment of the central nervous system. However, following transplantation Schwann cells show limited migratory ability and they are unable to intermingle with the host astrocytes.

Molecular control of brain plasticity and repair.

Recovery of function after damage to the CNS is limited due to the absence of axon regeneration and relatively low levels of plasticity. Plasticity in the CNS can be reactivated in the adult CNS by treatment with chondroitinase ABC, which removes glycosaminoglycan (GAG) chains from chondroitin sulfate proteoglycans (CSPGs). Plasticity in the adult CNS is restricted by perineuronal nets (PNNs) around many neuronal cell bodies and dendrites, which appear at the closure of critical periods and contain several inhibitory CSPGs.

Axonal mRNAs: characterisation and role in the growth and regeneration of dorsal root ganglion axons and growth cones.

We have developed a compartmentalised culture model for the purification of axonal mRNA from embryonic, neonatal and adult rat dorsal root ganglia. This mRNA was used un-amplified for RT-qPCR. We assayed for the presence of axonal mRNAs encoding molecules known to be involved in axon growth and guidance.

Bridging spinal cord injuries.

One strategy for spinal cord injury repair is to make cellular bridges that support axon regeneration. However, the bridging cells often fail to integrate with host tissue and may lead to increased pain sensitivity. Recent work has tested bridging with two forms of progenitor-derived astrocyte.

Role of extracellular factors in axon regeneration in the CNS: implications for therapy.

The glial scar that forms after an injury to the CNS contains molecules that are inhibitory to axon growth. Understanding of the mechanisms of inhibition has allowed the development of therapeutic strategies aimed at promoting axon regeneration. Promising results have been obtained in animal models, and some therapies are undergoing clinical trials.

Spinal cord repair: bridging the divide.

The normal spinal cord coordinates movement and sensation in the body. It is a complex organ containing nerve cells, supporting cells, and nerve fibers to and from the brain. The spinal cord is arranged in segments, with higher segments controlling movement and sensation in the upper parts of the body and lower segments controlling the lower parts of the body.

Heparan sulphate proteoglycans in glia and in the normal and injured CNS: expression of sulphotransferases and changes in sulphation.

Heparan sulphate proteoglycans (HSPGs) have multiple functions relevant to the control of the CNS injury response, particularly in modulating the effects of growth factors and localizing molecules that affect axon growth. We examined the pattern of expression and glycanation of HSPGs in the normal and damaged CNS, and in astrocytes and oligodendrocyte precursors because of their participation in the injury reaction. The composition of HS glycosaminoglycan (GAG) chains was analysed by biochemical analysis and by the binding of antibodies that recognize sulphated epitopes.

Chondroitinase ABC has a long-lasting effect on chondroitin sulphate glycosaminoglycan content in the injured rat brain.

Chondroitin sulphate proteoglycans (CSPGs) are axon growth inhibitory molecules present in the glial scar that play a part in regeneration failure after damage to the CNS and which restrict CNS plasticity. Removal of chondroitin sulphate glycosaminoglycan (GAG) chains with chondroitinase-ABC (chABC) in models of CNS injury promotes both axon regeneration and plasticity. We have analysed the immediate and long-term effects of a single injection of chABC on CSPGs, GAGs and axon regeneration.

Repair in the central nervous system.

The subject of central nervous system damage includes a wide variety of problems, from the slow selective 'picking off' of characteristic sub-populations of neurons typical of neurodegenerative diseases, to the wholesale destruction of areas of brain and spinal cord seen in traumatic injury and stroke. Experimental repair strategies are diverse and the type of pathology dictates which approach will be appropriate. Damage may be to grey matter (loss of neurons), white matter (cutting of axons, leaving neurons otherwise intact, at least initially) or both.

How does chondroitinase promote functional recovery in the damaged CNS?

A number of recent studies have established that the bacterial enzyme chondroitinase ABC promotes functional recovery in the injured CNS. The issue of how it works is rarely addressed, however. The effects of the enzyme are presumed to be due to the degradation of inhibitory chondroitin sulphate GAG chains.

Inosine promotes recovery of skilled motor function in a model of focal brain injury.

Recovery of function following traumatic brain injury (TBI) is partly through neuronal plasticity. However plasticity is limited in the adult CNS compared with young animals. In order to test whether treatments that enhance CNS plasticity might improve functional recovery after TBI, a new rat head injury model was developed, in which a computer-controlled impactor produced full thickness lesions of the forelimb region of the sensorimotor cortex.

Novel strategies for protection and repair of the central nervous system.

Clinical possibilities in many neurological conditions are limited by our current inability to correct structural damage to the nervous system, and treatments to prevent damage are also limited. Current research has produced promising treatments that promote neuroprotection, plasticity, axon regeneration, remyelination and cell replacement. As these treatments go through clinical trials and enter the clinic, the treatment of several neurological conditions will change greatly.

Guidelines for the conduct of clinical trials for spinal cord injury as developed by the ICCP panel: spontaneous recovery after spinal cord injury and statistical power needed for therapeutic clinical trials.

The International Campaign for Cures of Spinal Cord Injury Paralysis (ICCP) supported an international panel tasked with reviewing the methodology for clinical trials in spinal cord injury (SCI), and making recommendations on the conduct of future trials. This is the first of four papers. Here, we examine the spontaneous rate of recovery after SCI and resulting consequences for achieving statistically significant results in clinical trials.

Transplanted human neural precursor cells migrate widely but show no lesion-specific tropism in the 6-hydroxydopamine rat model of Parkinson's disease.

Parkinson's disease (PD), while primarily associated with degeneration of nigrostriatal dopamine neurons, is now increasingly recognized to have more widespread cell loss and so the most effective cell replacement therapy should target all these neuronal losses. Neural precursor cells might be ideal in this regard as in certain circumstances they have been shown to migrate widely following transplantation into the CNS. The aim of this study was to investigate whether transplanted human expanded neural precursor cells (hENPs) could migrate to sites of established or evolving pathology in the adult brain using the 6-hydroxydopamine (6-OHDA) rat model of PD.

The injury response of oligodendrocyte precursor cells is induced by platelets, macrophages and inflammation-associated cytokines.

Oligodendrocyte precursor cells recognized with the NG2 antibody respond rapidly to CNS injuries with hypertrophy and upregulation of the NG2 chondroitin sulfate proteoglycan within 24 h. These cells participate in glial scar formation, remaining around the injury site for several weeks. After injury, reactive oligodendrocyte precursor cells increase their production of several chondroitin sulfate proteoglycans, including NG2: this cell type thus represents a component of the inhibitory environment that prevents regeneration of axons in the injured CNS.