*3.1.1.2.1 Nimodipine*

Nimodipine is a dihydropyridinic Ca+2 channel antagonist that boosts the brain's blood flow, without compromising metabolism [26, 27]. It reduces malondialdehyde (MDA) levels, ED-1 markers for activated macrophages and myeloperoxidase (MPo). Studies have shown that nimodipine helps reducing FR, oxidative damage, resulting in the reduction of the damaged area and the infiltration of the inflammatory cells to the region, allowing SCI restoration [26]. Furthermore, the effect of inhibiting Ca+2 flux by nimodipine reduces apoptosis and tissue damage after SCI, increasing cell viability [27].

#### *3.1.2 Inhibitors of NMDA and AMPA-kainate receptors*

### *3.1.2.1 Memantine*

Memantine is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, which through the inhibition of hypoxic or ischemic damage/necrosis helps to prevent the secondary damage in SCI [28, 29]. The use of an NMDA antagonist limits neuronal glutamate exposure caused by excitatory amino acid neurotransmitters [29]. The use of memantine with anti-apoptotic agents like Q-VD-OPh boosts the neuroprotective effect through the reduction in apoptosis and necrosis mechanisms. Moreover, it provides better clinical and histological outcomes by limiting neuronal necrosis [28, 29].

#### *3.1.2.2 Gacyclidine*

Gacyclidine is a noncompetitive NMDA antagonist that is able to reduce the extension of ischemic lesions in SCI. It has been proven that gacyclidine is efficient in enhancing the functional and histological condition of the injury, but their neuroprotective effects are time and dose-dependent [30, 31].

#### *3.1.2.3 NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzoquinoxaline)*

NBQX is an AMPA/kainate antagonist that during acute SCI improves mitochondrial function and diminishes reactive oxygen species (ROS) formation as well as LPO production [32, 33]. The treatment with NBQX reduces white matter loss following SCI. Further studies are needed to know more about its efficacious effects in acute SCI.

#### *3.1.3 Inhibitors of free radicals and lipid peroxidation*

#### *3.1.3.1 Polyunsaturated fatty acids (PUFAs)*

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are structural compounds of the phospholipid membrane. They produce beneficial effects in neurodegenerative diseases by its anti-inflammatory, antioxidant, and membrane stabilizing properties [34]. ω-3 PUFAs, particularly docosahexaenoic acid (DHA), exert profound anti-inflammatory effects on the central nervous system (CNS), confer significant protection to the white matter, and help to increase neurite growth and synapse formation. DHA acts on cyclooxygenases (COX), cytosolic phospholipase A2 (cPLA2), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) [35, 36]. Deficiencies of lipids affect neural responses in CNS injuries, and this must predispose nerve cells to dysfunction [37]. According to previous findings, there are some investigations (**Table 1**) that have previously shown the effects of PUFAs in preclinical models.

#### *3.1.3.2 Glutathione*

Glutathione (GSH) is a tripeptide compound constituted by glutamine, glycine, and cysteine. The reduced form of GSH is glutathione-monoethyl-ester (GSHE), which is an endogenous, rechargeable antioxidant. Besides its anti-oxidant functions, GSHE plays a role in regulation of apoptosis, and it is important for

**163**

*Trends in Neuroprotective Strategies after Spinal Cord Injury: State of the Art*

**Treatment outcome Ref.**

ALA, combined with DHA, protects against neuronal necrosis and apoptosis. [39]

DHA plus rehabilitation enhance a functional, anatomical, and synaptic plasticity in cervical SCI. [42]

[34]

[38]

[40]

[37, 41]

α-linolenic acid (ALA) and DHA reduce lesion size and increase motor recovery and neuronal

DHA reduces microglia activation in both ventral and dorsal horns and increases motor recovery,

DHA induces a reduction in neutrophil number in SC epicenter. The administration confers

Prophylactic therapy with ω-3 has shown a reduction in cellular vulnerability. Supporting functional recovery, there is also an increase in levels of protein kinase B/Akt and CREB.

cellular defense against ROS [43, 44]. Some studies have reported that GSHE diminishes SC LPO after SCI, while also acting as a vasodilator under conditions of oxidative stress [44, 45]. In addition, GSHE plays an anti-excitotoxic role by inhibiting the binding ligands to ionotropic glutamate receptors under redox modulation, which have been involved in excitotoxicity after SCI. As a consequence of the reduction of GSH after an injury, there is neuronal loss in the SC, probably due to oxidative stress and mitochondrial dysfunction. Combined therapy of GSHE with A91 resulted in a better motor recovery and axonal sparing associated with a higher axonal myelination [46]. The use of GSHE could be an interesting alternative for SCI therapy; however, it should be strongly evaluated before its use in clinical trials.

Caspase inhibitor Z-DEVD-fmk is a selective caspase-3 inhibitor that also has antiinflammatory properties. Anti-apoptosis compounds are used to block apoptotic cell death but also to inhibit cytokine production. Treatment of SCI with z-DEVD reduces secondary tissue damage, ischemic injury, preserves motor function, and provides neuroprotection via the inhibition of cell death in all of cell types in the SC [47, 48]. Low doses of z-DEVD-fmk combined with basic fibroblast growth factor (bFGF) reduce neurological deficit in ischemia, therefore providing neuroprotection [49].

Caspase inhibitor z-LEHD-fmk acts as a selective caspase-9 inhibitor with antiapoptotic properties. This drug helps decreasing levels of apoptosis biochemical markers, reducing lesion size and remaining active during treatment to maintain its therapeutic effect. Treatment with z-LEHD-fmk helps to prevent apoptosis in a variety of cell types like neurons, astrocytes, oligodendrocytes, and microglia populations [50]. Further studies are needed to understand more about its effects

Calpains belong to the family of calcium-dependent nonlysosomal cysteine proteases, which can be found expressed through the CNS. They are involved in

*DOI: http://dx.doi.org/10.5772/intechopen.89539*

promoting beneficial functional effect in SCI.

*Polyunsaturated fatty acids in spinal cord injury.*

histological protection and improves motor recovery.

survival.

**Table 1.**

*3.1.4 Anti-apoptosis therapy*

*3.1.4.1 Zdevd-fmk*

*3.1.4.2 z-LEHD-fmk*

and benefits in acute SCI.

*3.1.5 Calpain inhibitors*

*Trends in Neuroprotective Strategies after Spinal Cord Injury: State of the Art DOI: http://dx.doi.org/10.5772/intechopen.89539*


#### **Table 1.**

*Neuroprotection - New Approaches and Prospects*

*3.1.2.1 Memantine*

neuronal necrosis [28, 29].

*3.1.2.2 Gacyclidine*

in acute SCI.

preclinical models.

*3.1.3.2 Glutathione*

*3.1.2 Inhibitors of NMDA and AMPA-kainate receptors*

Memantine is a noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonist, which through the inhibition of hypoxic or ischemic damage/necrosis helps to prevent the secondary damage in SCI [28, 29]. The use of an NMDA antagonist limits neuronal glutamate exposure caused by excitatory amino acid neurotransmitters [29]. The use of memantine with anti-apoptotic agents like Q-VD-OPh boosts the neuroprotective effect through the reduction in apoptosis and necrosis mechanisms. Moreover, it provides better clinical and histological outcomes by limiting

Gacyclidine is a noncompetitive NMDA antagonist that is able to reduce the extension of ischemic lesions in SCI. It has been proven that gacyclidine is efficient in enhancing the functional and histological condition of the injury, but their

NBQX is an AMPA/kainate antagonist that during acute SCI improves mitochondrial function and diminishes reactive oxygen species (ROS) formation as well as LPO production [32, 33]. The treatment with NBQX reduces white matter loss following SCI. Further studies are needed to know more about its efficacious effects

Omega-3 polyunsaturated fatty acids (ω-3 PUFAs) are structural compounds of the phospholipid membrane. They produce beneficial effects in neurodegenerative diseases by its anti-inflammatory, antioxidant, and membrane stabilizing properties [34]. ω-3 PUFAs, particularly docosahexaenoic acid (DHA), exert profound anti-inflammatory effects on the central nervous system (CNS), confer significant protection to the white matter, and help to increase neurite growth and synapse formation. DHA acts on cyclooxygenases (COX), cytosolic phospholipase A2 (cPLA2), and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-kB) [35, 36]. Deficiencies of lipids affect neural responses in CNS injuries, and this must predispose nerve cells to dysfunction [37]. According to previous findings, there are some investigations (**Table 1**) that have previously shown the effects of PUFAs in

Glutathione (GSH) is a tripeptide compound constituted by glutamine, glycine, and cysteine. The reduced form of GSH is glutathione-monoethyl-ester (GSHE), which is an endogenous, rechargeable antioxidant. Besides its anti-oxidant functions, GSHE plays a role in regulation of apoptosis, and it is important for

neuroprotective effects are time and dose-dependent [30, 31].

*3.1.3 Inhibitors of free radicals and lipid peroxidation*

*3.1.3.1 Polyunsaturated fatty acids (PUFAs)*

*3.1.2.3 NBQX (2,3-dihydroxy-6-nitro-7-sulfamoylbenzoquinoxaline)*

**162**

*Polyunsaturated fatty acids in spinal cord injury.*

cellular defense against ROS [43, 44]. Some studies have reported that GSHE diminishes SC LPO after SCI, while also acting as a vasodilator under conditions of oxidative stress [44, 45]. In addition, GSHE plays an anti-excitotoxic role by inhibiting the binding ligands to ionotropic glutamate receptors under redox modulation, which have been involved in excitotoxicity after SCI. As a consequence of the reduction of GSH after an injury, there is neuronal loss in the SC, probably due to oxidative stress and mitochondrial dysfunction. Combined therapy of GSHE with A91 resulted in a better motor recovery and axonal sparing associated with a higher axonal myelination [46]. The use of GSHE could be an interesting alternative for SCI therapy; however, it should be strongly evaluated before its use in clinical trials.

#### *3.1.4 Anti-apoptosis therapy*

## *3.1.4.1 Zdevd-fmk*

Caspase inhibitor Z-DEVD-fmk is a selective caspase-3 inhibitor that also has antiinflammatory properties. Anti-apoptosis compounds are used to block apoptotic cell death but also to inhibit cytokine production. Treatment of SCI with z-DEVD reduces secondary tissue damage, ischemic injury, preserves motor function, and provides neuroprotection via the inhibition of cell death in all of cell types in the SC [47, 48]. Low doses of z-DEVD-fmk combined with basic fibroblast growth factor (bFGF) reduce neurological deficit in ischemia, therefore providing neuroprotection [49].

#### *3.1.4.2 z-LEHD-fmk*

Caspase inhibitor z-LEHD-fmk acts as a selective caspase-9 inhibitor with antiapoptotic properties. This drug helps decreasing levels of apoptosis biochemical markers, reducing lesion size and remaining active during treatment to maintain its therapeutic effect. Treatment with z-LEHD-fmk helps to prevent apoptosis in a variety of cell types like neurons, astrocytes, oligodendrocytes, and microglia populations [50]. Further studies are needed to understand more about its effects and benefits in acute SCI.

#### *3.1.5 Calpain inhibitors*

Calpains belong to the family of calcium-dependent nonlysosomal cysteine proteases, which can be found expressed through the CNS. They are involved in neurodegeneration, degradation of cytoskeleton, and apoptosis via caspase-3 due to its proteolytic activities, in SCI. The influx of Ca+2 stimulates Ca+2-dependent enzymes, within them are calpains, which seem to play a role in proteolysis by contributing to apoptosis in CNS cells. The cell death decreases mRNA expression and transcription of myelin basic protein (MBP) and proteolipid protein (PLP), which are axonal neurofilament proteins [49, 51, 52]. The administration of a calpain inhibitor such as E-64-d (1 mg/kg) to injured rats blocks apoptosis and helps to re-establish MBP and PLP genes [51]. The administration of other calpain inhibitors such as SJA 6017 and calpeptin has demonstrated their ability to induce neuroprotection after SCI [53, 54]. Despite the study efforts and the promising therapeutic effects for functional neuroprotection, there are no clinical trials testing these drugs, so further studies are needed for the use of calpain inhibitors in patients.
