**3. Neuroprotection in the CNS**

Neuroprotection is defined as a curative strategy against harmful biochemical and molecular lesions that, if left untreated, lead to CNS damage [29]. The main purpose is to protect the damaged area by modifying the pathophysiological cascade with the limitation of harmful processes at secondary damage. In particular, the objective is to save those cell populations that are not directly affected by the injury, but due to secondary processes will underlay delayed apoptosis [45, 46]. In this regard, the primary goal is to suppress secondary inflammatory processes, edema and hemorrhage, and excitotoxicity that expand from the lesion center above and below the lesion site and acts destructively on healthy cells. Neuroprotection is among the specific therapies used in CNS injuries [47].

One of the important concepts that have recently resonated is the use of neuroprotective strategies that are applied to the spinal cord in conjunction with clinically proven operative methods of decompression and reconstruction of the spine. This clearly indicates that early intervention on traumatic spinal cord injuries can significantly affect the prognosis of the disease [3]. Therefore, great attention has been paid to studies that deal with the optimal timing of surgical procedures for acute spinal cord injury [48]. Previous data suggest that patients undergoing surgical decompression within 24 h after spinal cord injury have a significantly better recovery prognosis [29]. Currently, a number of innovative neuroprotective strategies for acute spinal cord injuries are being tested and evaluated in randomized controlled trials. Experimental studies on animal models showing promising results, such as ChABC, minocycline, riluzole, granulocyte colony stimulating factor (G-CSF), are now being tested in clinical studies [2, 49]. Hypothermia induced by intravascular cooling infusion administered epidural or subcutaneously has achieved success during acute SCI treatment.

#### **3.1. Pharmacotherapy**

protein 5), Negr1 (neuronal growth regulator 1), NCAN (neurocan core protein), CD44, Wnt8, syndecan-4, nexin, and Bcl-2, were identified. Specific factors involved in immune cell chemotaxis or cellular adhesion, including complement factors (C1qb, C1qc, factor D, factor I, and

In contrast, proteins produced in the caudal region were related to necrosis factors (BAX, BAD, Caspase 6, and neogenin), cytoskeleton proteins, synaptic vesicle exocytosis, chemoat-

These data are in line with our previous *in vivo* results demonstrating that neurite outgrowth takes place from rostral to lesion but never in the opposite direction from caudal to the lesion. Furthermore, the presence of chemokines, lectins, and growth factors in the rostral but not in the caudal segment clearly document the immediate inflammatory response together with

In order to investigate the neurotrophic role of CM derived from the injured tissue, studies testing neurite outgrowth in rat DRG explants have been undertaken. Data from these experiments confirmed that enhanced neurite sprouting of DRGs facilitated by CM from rostral and lesion segments were most likely mediated by the content of neurotrophic factors, i.e., FGF-1, NGF, PGF, BMP 2 or BMP3, GAP-43, neurotrimin, neurofascin, and other molecules involved in neuronal development/differentiation/migration. Although the principal role of NGF/TrkA pathways in sensory axon outgrowth has been widely demonstrated, other neurotrophic factors including the BMPs (members of the TGFβ superfamily) or GAP-43 have to be taken into account [41, 44]. In summary, it has been demonstrated that few days after SCI, a clear regionalization occurs between the rostral and caudal axes, with expression of neurotrophic and immunomodulatory factors in the rostral region, in contrast to inflammatory and apoptotic molecules in the caudal region. These data indicate the importance of stimulating neurite sprouting at segments below the lesion by inhibiting inflammation and turning polarization of M1 cells to the M2 state, which could have a clear impact on neurorepair. Therefore, these findings should be

Neuroprotection is defined as a curative strategy against harmful biochemical and molecular lesions that, if left untreated, lead to CNS damage [29]. The main purpose is to protect the damaged area by modifying the pathophysiological cascade with the limitation of harmful processes at secondary damage. In particular, the objective is to save those cell populations that are not directly affected by the injury, but due to secondary processes will underlay delayed apoptosis [45, 46]. In this regard, the primary goal is to suppress secondary inflammatory processes, edema and hemorrhage, and excitotoxicity that expand from the lesion center above and below the lesion site and acts destructively on healthy cells. Neuroprotection is

One of the important concepts that have recently resonated is the use of neuroprotective strategies that are applied to the spinal cord in conjunction with clinically proven operative methods

CD59), tetraspanins (CD9 and CD82), and CD14 have also been characterized [40, 41].

tractant factors, and neuronal postsynaptic density.

8 Essentials of Spinal Cord Injury Medicine

activity-dependent factors released by neurons and glia.

taken into account when planning new treatment strategies.

among the specific therapies used in CNS injuries [47].

**3. Neuroprotection in the CNS**

Pharmacotherapy is one of the most widespread forms of treating secondary damage that use a wide variety of different types of molecules to target specific secondary processes. These are comprised of anti-inflammatory or neurostimulating compounds such as, minocycline, neurotrophic factors (BDNF, GDNF, NGF, and erythropoietin), and molecules that alleviate regenerating axons from the inhibitory effects of extracellular matrix molecules.

In particular, chondroitinase ABC eliminate CSPG with the major component NG2 which inhibits the regeneration of damaged axons [50]. Nogo-neutralizing antibodies or blockers of the post-receptors components RhoA, are used to improve long-distance axon regeneration and sprouting [25]. Previous studies have identified Rho pathway as important to control the neuronal response after CNS injury. Therefore, a drug called Cethrin® that blocks activation of Rho is actually in phase I/IIa of clinical trials [48]. The most encouraging findings were observed in patients with cervical SCI, whereas patients with injuries at thoracic level received only modest neurological recovery. Although the patient numbers were small in this trial, the results obtained indicate some evidence of efficacy to enhance functional recovery and warrant further clinical trials [51].

#### **3.2. Molecular therapies: chondroitinase ABC, minocycline, tacrolimus, riluzole**

**Chondroitinase ABC** is a bacterial enzyme that reduces the inhibitory effect of CSPGs at the site of injury. In order to increase CNS regeneration, only chondroitinase ABC purified from Proteus vulgaris [52] should be delivered. The mechanism of action lies in removing GAG chains from the nuclear protein and converting them to unsaturated disaccharides [34]. These stimulate the release of growth factors and proteins attached to GAGs of CSPGs, thereby enabling their diffusion and interaction with neural cell receptors. ChABC has been shown to promote neuroprotection and neuroregeneration [53]. Experimental administration of ChABC after cervical SCI positively affects the branching of damaged and intact descending pathways around which increased accumulation of CSPGs and then inhibition of axonal growth occurs. The neuroprotective effect of ChABC has been described also for the hemisection of the spinal cord [50, 54], transection of dorsal columns [55], and after compression injury of the thoracic spinal cord and the peripheral nerve [56] or in adult rats with visual deficits [57].ChABC administration is often combined with other therapeutic elements such as LiCl or Schwann cell transplantation [58] that can trigger regeneration. On the other hand, axonal plasticity supported by histological analyses did not correlate with motor function improvements of hind limbs. A similar conclusion was obtained by a group led by Cafferty [59]. There are several explanations for the negative correlation between the growths of axons without functional enhancements.

crosses the blood–brain barrier [62]. This drug has been shown to be beneficial in various experimental animal models of CNS diseases. Primary mechanisms of action lie on the inhibition of microglia activation, which would justify its potential effectiveness in the treatment of neuroinflammatory and/or neurodegenerative disorders [63]. Different *in vitro* studies have described minocycline's ability to block LPS-stimulated inflammatory cytokine secretion and Toll-like-receptor (TLR)-2 surface expression in the BV-2 cell line and on primary microglia isolated from the brains of adult mice. Minocycline also attenuated the mRNA expression of inflammatory genes, including IL-6, IL-1β, major histocompatibility complex (MHC) II, and TLR-2. In experimental models of SCI, minocycline delivery significantly improved the function and strength of both hindlimbs, reduced the gross lesion size in the spinal cord, and enhanced axonal sparing. Minocycline-treated rats showed decreased release of cytochrome c from the mitochondria, resulting in markedly enhanced long-term hindlimb locomotion [64]. In traumatic SCI, results [65] showed that both short and long-term treatment with minocycline had a neuroprotective effect on the spinal cord segments located rostral to the injury epicenter. Minocycline has also been shown to improve functional recovery after SCI through the inhibition of pro-nerve growth factor production by microglia, thereby reducing oligodendrocyte death and apoptosis after traumatic SCI. It has been shown to inhibit the expression of p75 neurotrophin receptor and the activation of the Ras homolog gene family, member A (RhoA) after SCI [61]. Furthermore, previous study reported that minocycline might also exert a neuroprotective effect in SCI by inhibiting caspase expression and matrix metalloproteinases [65]. Metalloproteinases belong to a group of proteases that are responsible for the degradation and remodeling of the individual components of the intracellular matrix in normal tissue, and their activity is regulated by endogenous inhibitors. However, many pathological CNS conditions are characterized by increased metalloproteinase activity due to the reduced activity of their tissue inhibitors. The imbalance between intracellular matrix metalloproteinases and their inhibitors may lead to destructive proteolytic damage to the CNS tissue [45]. Minocycline has shown beneficial effects in many experimental studies [65] and was therefore also approved for phase I and II clinical trials in patients with completely injured spinal cord. The overall results confirmed the safety of the drug, but did not show improved motor outcomes in patients treated with minocycline compared to placebo. However, in a subset of patients with incomplete spinal cord injuries, patients experienced significant improvement [66]. Based on this promising outcome, a Phase III clinical trial was initiated in patients with

Understanding Molecular Pathology along Injured Spinal Cord Axis: Moving Frontiers…

http://dx.doi.org/10.5772/intechopen.72118

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acute spinal cord injury. This is currently ongoing and will be completed in 2018 [67].

Another interesting formulation is **FK506** (tacrolimus) isolated from the bacterium *Streptomyces tsukubaensis*, which presents a potent immunosuppressive drug. Primarily, it is used to reduce allograft rejection in organ transplantation, but also offers neuroprotective properties for central nervous system trauma. FK506 blocks the activation of calcineurin through the formation of complexes with immunophilins. However, it binds to a different immunophilin than cyclosporine A (CsA) [68]. FK506 has been found to increase nerve regeneration and functional re-innervation after peripheral nerve injury, as well as prevent axonal damage in toxic neuropathies [69]. Several studies document that FK506 delivery protects tissue from secondary injury and showed a beneficial effect during an acute SCI [70]. However, long-term administration of FK506 after experimental spinal cord injury in rats has shown to be not as effective [71]. FK506 was also used as a potent inhibitor of activated T-cells that infiltrates the injured spinal cord. Thus, it can modulate inflammation and ameliorate neuroprotection through its immunosuppressive

#### *3.2.1. Orientation and quantity of functional synaptic connections*

Functional recovery is dependent on correct orientation of axons and their functional links to the target structure. In some studies, linearly oriented as well as disordered nerve fibers that regrow through the lesion in different directions have been observed. Theoretically, they might increase the plasticity of tissues, because they cover a broader area. On the other hand, disorganized nerve fibers are often losing functional links with the target structure [60].
