*3.2.3. Method of ChABC administration*

The important factors that affect the efficiency of ChABC therapy are: (i) method of local delivery, (ii) dose, (iii) timing of therapy, and (iv) efficacy of ChABC, since it is a bacterial enzyme which loses its activity *in vivo*. Therefore, to ensure its activity, repeated intrathecal delivery of ChABC or thermostable ChABC should be considered.

The undesirable effects of ChABC delivery have been observed only in rare cases. They are often related to the immune response against the enzyme or to neoepitopes (cleavage products) that this bacterial enzyme forms. Despite the rare negative effects, ChABC broadly reorganizes extracellular matrix, changes cell adhesion and tissue diffusion, and stimulates the functional recovery of damaged CNS [38].

In summary, the results confirmed that early reduction of NG2 allows extracellular matrix reorganization, creating a favorable environment for the initial neuroprotective processes to enable significant regrowth of injured axons in the epicenter of damage. Experimental studies also demonstrate that in order to achieve a better neurological outcome, ChABC needs to be combined with other therapeutic approaches. These may increase the plasticity of the injured tissue, create an environment for the axon outgrowth of fibers, and navigate these fibers to the right direction for the creation of fully functional synaptic connections.

**Minocycline** is a second-generation, semisynthetic tetracycline that has been commonly used in the treatment of acne vulgaris in children, because of its antibiotic properties against both gram-positive and gram-negative bacteria. However, it has been shown that minocycline can exert a variety of biological actions that are independent of their anti-microbial activity, including anti-inflammatory and anti-apoptotic activities, inhibition of proteolysis, angiogenesis, and tumor metastasis. Minocycline reveals high lipid solubility [61] and therefore easily 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 acute spinal cord injury. This is currently ongoing and will be completed in 2018 [67].

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 correla-

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

Another possible negative factor that influenced clinical outcome may be the short-term survival of experimental animals required for functional contact formations. The intensive regeneration process in human patients progresses for months or years, and it is therefore necessary to prolong the length of survival in experimental animals from 3 to 6 months.

The important factors that affect the efficiency of ChABC therapy are: (i) method of local delivery, (ii) dose, (iii) timing of therapy, and (iv) efficacy of ChABC, since it is a bacterial enzyme which loses its activity *in vivo*. Therefore, to ensure its activity, repeated intrathecal delivery of

The undesirable effects of ChABC delivery have been observed only in rare cases. They are often related to the immune response against the enzyme or to neoepitopes (cleavage products) that this bacterial enzyme forms. Despite the rare negative effects, ChABC broadly reorganizes extracellular matrix, changes cell adhesion and tissue diffusion, and stimulates the functional

In summary, the results confirmed that early reduction of NG2 allows extracellular matrix reorganization, creating a favorable environment for the initial neuroprotective processes to enable significant regrowth of injured axons in the epicenter of damage. Experimental studies also demonstrate that in order to achieve a better neurological outcome, ChABC needs to be combined with other therapeutic approaches. These may increase the plasticity of the injured tissue, create an environment for the axon outgrowth of fibers, and navigate these fibers to the right

**Minocycline** is a second-generation, semisynthetic tetracycline that has been commonly used in the treatment of acne vulgaris in children, because of its antibiotic properties against both gram-positive and gram-negative bacteria. However, it has been shown that minocycline can exert a variety of biological actions that are independent of their anti-microbial activity, including anti-inflammatory and anti-apoptotic activities, inhibition of proteolysis, angiogenesis, and tumor metastasis. Minocycline reveals high lipid solubility [61] and therefore easily

tion between the growths of axons without functional enhancements.

nerve fibers are often losing functional links with the target structure [60].

*3.2.1. Orientation and quantity of functional synaptic connections*

*3.2.2. The time required for the maturation of functional linkages*

ChABC or thermostable ChABC should be considered.

direction for the creation of fully functional synaptic connections.

*3.2.3. Method of ChABC administration*

10 Essentials of Spinal Cord Injury Medicine

recovery of damaged CNS [38].

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 action on immune cells [72]. Furthermore, the immunosuppressive action of FK506 was proven by the prevention of graft rejection following spinal cord ischemia and SCI [44].

Among different **mono-therapies**, more **complex cellular therapy** has reached considerable attention due to targeting multiple aims, such as bridging the cavities or cysts, replacing dead

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

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

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SCI results in cysts or cavities at the site of the lesion, which gradually expand in the caudal direction. From this point of view, cell therapy alone for such a progressive pathological process as SCI is insufficient. Therefore, it is recommended to combine the administration of stem cells with biodegradable biomaterials that fill the cavities. The main objective is to optimize mechanical properties, cell adhesion, and biodegradability of synthetic or natural materials and develop new methods to deliver cells to the lesion site. One of the most important features for the successful integration of the implant into damaged tissue of the spinal cord is its optimal mechanical strength. If the biomaterial is too rigid, it can cause compression of regenerating axons and the formation of additional secondary cavities between the implant and surrounding spinal tissue. Therefore, it is preferable to use an injectable biomaterial that can properly adapt to the lesion [63, 77].The stem cells with which the implant should colonize also require the presence of growth factors that help them to survive in the unfavorable environment of the injured spinal cord. Chen and his scientific group compared the regenerative capabilities of several biodegradable multichannel biomaterials with different mechanical properties that were colonized by Schwann cells and implanted into the spinal cord after transection [63]. Compared to the poly-caprolactone fumarate material, which had significantly higher compression modulus values, biomaterials based on hydrogels showed significantly smaller cavities and promoted material vascularization and Schwann cell infiltration [63].

The biomaterial has to be biocompatible; this depends on the properties of the surface of the material and its interactions with cells or proteins [78]. However, we have to be aware of non-specific inflammatory responses of the recipient to the foreign biomaterial, and its extent determines the rate of implant biocompatibility. Interestingly, the acute response of the immune system that is mediated by macrophages or dendritic cells can be neuroprotective and can promote CNS regeneration. Modulation of the inflammatory response by the type of biomaterial surface can therefore be an auxiliary tool for repair mechanisms of the tissue. In principle, the physical properties of biomaterials should simulate the extracellular environment of the central nervous system and thereby ensure the diffusion of neurotrophic factors. Interactions between biomaterial surface and living tissue are usually mediated by a layer of proteins. Most biomaterials have an optimized surface with bioactive molecules or oligopeptide sequences [77]. This guarantees the adhesion of specific cells or their parts (e.g., axons). **Biodegradable** materials are more desirable than non-degradable ones. Their degradation is most often mediated by hydrolysis and enzymatic cleavage. The rate of degradation can be controlled by various factors, such as molecular weight and polymer structure, crosslinking, and use of copolymers [79]. Of course, degradation products must not cause any immune response and the rate of breakdown of the material must be appropriate to the formation of new tissue. Biomaterials that are used to regenerate nerve tissue usually degrade for weeks or months, depending on the axonal and vascular material growth. Degradation can take place by gradual erosion of the surface of the material while maintaining the structural integrity of the material

cells, and creating a favorable environment allowing axonal regeneration [76].

**4.1. Regenerative approaches toward biomaterials**

**Riluzole** is commonly used in the treatment of amyotrophic lateral sclerosis (ALS) to protect against nerve cell degeneration. The possible mechanism of action of riluzole is blocking sodium channels as well as glutamate excitotoxicity. The deleterious effect of glutamate overproduction during CNS damage can be reduced by both reducing the synthesis and preventing its release into the synaptic cleft. In the case of riluzole, its mechanism of action is most likely thought to be the reduction of glutamate synthesis and thereby its release into the presynaptic region of the neuron. In a recent study, 155 patients were randomized to riluzole treatment (100 mg/day) or to placebo. The patients were monitored for 12–21 months [48]. Survival was significantly longer in the riluzole-treated group compared to placebo-treated patients. The median survival time was 17.7 months for riluzole compared to 14.9 months for placebo [4]. Additionally, there was a significant improvement in motor function in patients with cervical SCI receiving 50 mg riluzole twice a day for 14 days after injury, compared to the control group [73].
