Neuroprotective Effects of Recombinant Thrombomodulin in Controlled Contusion Spinal Cord Injury Implicates Thrombin Signaling

Thrombin Priming Promotes the Neuroprotective Effects of Human Wharton's Jelly-Derived Mesenchymal Stem Cells Via the HGF/AKT/STAT3 Signaling Pathway

Mesenchymal stem cells (MSCs) directly differentiate into neurons and endothelial cells after transplantation, and their secretome has considerable potential for treating brain injuries. Previous studies have suggested that the effects of MSCs priming with exposure to hypoxia, cytokines, growth factors, or chemical agents could optimize the paracrine potency and therapeutic potential of MSCs. Studies have suggested that thrombin-primed Wharton's Jelly-derived mesenchymal stem cells (Th.WJ-MSCs) significantly enhance the neuroprotective beneficial effects of naive MSCs in brain injury such as hypoxic-ischemic brain injury (HIE) and intraventricular hemorrhage (IVH). This study aimed to characterize WJ-MSCs in terms of stem cell markers, differentiation, cell proliferation, and paracrine factors by comparing naive and Th.WJ-MSCs. We demonstrated that compared with naive MSCs, Th.MSCs significantly enhanced the neuroprotective effects in vitro. Moreover, we identified differentially expressed proteins in the conditioned media of naive and Th.WJ-MSCs by liquid chromatography-tandem mass spectrometry analysis. Secretome analysis of the conditioned medium of WJ-MSCs revealed that such neuroprotective effects were mediated by paracrine effects with secretomes of Th.WJ-MSCs, and hepatocyte growth factor was identified as a key paracrine mediator. These results can be applied further in the preclinical and clinical development of effective and safe cell therapeutics for brain injuries such as HIE and IVH.

The thrombin receptor modulates astroglia-neuron trophic coupling and neural repair after spinal cord injury

Excessive activation of the thrombin receptor, protease activated receptor 1 (PAR1) is implicated in diverse neuropathologies from neurodegenerative conditions to neurotrauma. PAR1 knockout mice show improved outcomes after experimental spinal cord injury (SCI), however information regarding the underpinning cellular and molecular mechanisms is lacking. Here we demonstrate that genetic blockade of PAR1 in female mice results in improvements in sensorimotor co-ordination after thoracic spinal cord lateral compression injury. We document improved neuron preservation with increases in Synapsin-1 presynaptic proteins and GAP43, a growth cone marker, after a 30 days recovery period. These improvements were coupled to signs of enhanced myelin resiliency and repair, including increases in the number of mature oligodendrocytes, their progenitors and the abundance of myelin basic protein. These significant increases in substrates for neural recovery were accompanied by reduced astrocyte (Serp1) and microglial/monocyte (CD68 and iNOS) pro-inflammatory markers, with coordinate increases in astrocyte (S100A10 and Emp1) and microglial (Arg1) markers reflective of pro-repair activities. Complementary astrocyte-neuron co-culture bioassays suggest astrocytes with PAR1 loss-of-function promote both neuron survival and neurite outgrowth. Additionally, the pro-neurite outgrowth effects of switching off astrocyte PAR1 were blocked by inhibiting TrkB, the high affinity receptor for brain derived neurotrophic factor. Altogether, these studies demonstrate unique modulatory roles for PAR1 in regulating glial-neuron interactions, including the capacity for neurotrophic factor signaling, and underscore its position at neurobiological intersections critical for the response of the CNS to injury and the capacity for regenerative repair and restoration of function.

The thrombin receptor links brain derived neurotrophic factor to neuron cholesterol production, resiliency and repair after spinal cord injury

Despite concerted efforts to identify CNS regeneration strategies, an incomplete understanding of how the needed molecular machinery is regulated limits progress. Here we use models of lateral compression and FEJOTA clip contusion-compression spinal cord injury (SCI) to identify the thrombin receptor (Protease Activated Receptor 1 (PAR1)) as an integral facet of this machine with roles in regulating neurite growth through a growth factor- and cholesterol-dependent mechanism. Functional recovery and signs of neural repair, including expression of cholesterol biosynthesis machinery and markers of axonal and synaptic integrity, were all increased after SCI in PAR1 knockout female mice, while PTEN was decreased. Notably, PAR1 differentially regulated HMGCS1, a gene encoding a rate-limiting enzyme in cholesterol production, across the neuronal and astroglial compartments of the intact versus injured spinal cord. Pharmacologic inhibition of cortical neuron PAR1 using vorapaxar in vitro also decreased PTEN and promoted neurite outgrowth in a cholesterol dependent manner, including that driven by suboptimal brain derived neurotrophic factor (BDNF). Pharmacologic inhibition of PAR1 also augmented BDNF-driven HMGCS1 and cholesterol production by murine cortical neurons and by human SH-SY5Y and iPSC-derived neurons. The link between PAR1, cholesterol and BDNF was further highlighted by demonstrating that the deleterious effects of PAR1 over-activation are overcome by supplementing cultures with BDNF, cholesterol or by blocking an inhibitor of adenylate cyclase, Gαi. These findings document PAR1-linked neurotrophic coupling mechanisms that regulate neuronal cholesterol metabolism as an important component of the machinery regulating CNS repair and point to new strategies to enhance neural resiliency after injury.

Thrombin and the Coag-Inflammatory Nexus in Neurotrauma, ALS, and Other Neurodegenerative Disorders

This review details our current understanding of thrombin signaling in neurodegeneration, with a focus on amyotrophic lateral sclerosis (ALS, Lou Gehrig's disease) as well as future directions to be pursued. The key factors are multifunctional and involved in regulatory pathways, namely innate immune and the coagulation cascade activation, that are essential for normal nervous system function and health. These two major host defense systems have a long history in evolution and include elements and regulators of the coagulation pathway that have significant impacts on both the peripheral and central nervous system in health and disease. The clotting cascade responds to a variety of insults to the CNS including injury and infection. The blood brain barrier is affected by these responses and its compromise also contributes to these detrimental effects. Important molecules in signaling that contribute to or protect against neurodegeneration include thrombin, thrombomodulin (TM), protease activated receptor 1 (PAR1), damage associated molecular patterns (DAMPs), such as high mobility group box protein 1 (HMGB1) and those released from mitochondria (mtDAMPs). Each of these molecules are entangled in choices dependent upon specific signaling pathways in play. For example, the particular cleavage of PAR1 by thrombin vs. activated protein C (APC) will have downstream effects through coupled factors to result in toxicity or neuroprotection. Furthermore, numerous interactions influence these choices such as the interplay between HMGB1, thrombin, and TM. Our hope is that improved understanding of the ways that components of the coagulation cascade affect innate immune inflammatory responses and influence the course of neurodegeneration, especially after injury, will lead to effective therapeutic approaches for ALS, traumatic brain injury, and other neurodegenerative disorders.

The Effect of Neuronal Activity on Glial Thrombin Generation

Thrombin through its receptor PAR-1 plays an important role in the peripheral nervous system. PAR-1 is located at the microvilli of Schwann cells at the node of Ranvier, and thrombin is generated by the coagulation system on these glial structures. In the present study, we examined the link between neuronal activity and modulation of thrombin generation by glial Schwann cells. Thrombin activity was assessed in sciatic nerves in reaction to high KCl as a model of neuronal activity. We demonstrated a significant transient effect of high KCL on thrombin activity (F(5, 20) = 42.65, p < 0.0001, by ANOVA) compared to normal KCl levels. Since the sciatic nerve includes components of axons and Schwann cell myelin sheath, we continued to investigate the effect of high KCl on a Schwannoma cell line as a model for nodal Schwann cell microvilli. We demonstrated a transient decrease in thrombin activity in response to high extracellular KCl (F(1, 18) = 9.56, p = 0.0063). The major neuronal inhibitor of thrombin is PN-1, and we therefore measured the effect of high KCL on PN-1 immunofluorescence intensity. We found significantly higher PN-1 staining intensity 3 min after the application of high KCL in comparison to cells exposed to high KCL for 7 min and to cells in regular KCL (F(2, 102) = 8.4737, p < 0.0004), and this effect may explain the changes in thrombin activity. The present results support an interaction between neuronal activity and the coagulation pathway as a novel mechanism for neuron-glia crosstalk at the node of Ranvier.

Nafamostat mesilate attenuates inflammation and apoptosis and promotes locomotor recovery after spinal cord injury

AIM

Spinal cord injury (SCI) leads to severe neural damage for which there is currently no effective treatment. Exploration of the neuroprotective effect among clinically approved drugs will speed up clinical translation of SCI. Nafamostat mesilate (NM) as a synthetic serine protease inhibitor has been used clinically in pancreatitis treatments. However, its effectiveness in SCI is unknown. The aim of this study was to confirm the efficacy of NM in ameliorating SCI.

METHODS

Intraperitoneal administration of NM was performed on a contusion SCI model in Wistar rat. Hematoxylin and eosin staining (H&E staining) and Luxol fast blue (LFB) staining were used to observe the histological lesions. Apoptosis was examined by TUNEL staining, Annexin V-FITC/PI, caspase-3, and Bcl-2. Cytokines and neurotrophins were tested by Western blot. Locomotion recovery assessed by hindlimb BBB score and the inclined plane test.

RESULTS

Nafamostat mesilate treatment significantly improved locomotion recovery as assessed by hindlimb BBB scores and the inclined plane test. H&E staining and LFB staining showed a significant increase in spared tissue in both gray matter and white matter. NM decreased the expression of the proinflammatory cytokines TNF-α and IL-6. In addition, apoptosis was also significantly decreased, as shown by TUNEL staining and Annexin V-FITC/PI and by Western blotting for caspase-3 and Bcl-2 expression. Due to the mechanism of action of NM as a serine protease inhibitor, the drug decreased thrombin expression in the damaged spinal cord. Furthermore, NM increased the expression of neurotrophins (NT-3, BDNF, and NGF).

CONCLUSIONS

Upon NM treatment, the functional and histological outcomes were improved, and microenvironment upon SCI was modulated. As a clinically approved drug, NM holds promise for clinical use after spinal cord injury.

Proximate Mediators of Microvascular Dysfunction at the Blood-Brain Barrier: Neuroinflammatory Pathways to Neurodegeneration

Current projections are that by 2050 the numbers of people aged 65 and older with Alzheimer's disease (AD) in the US may increase threefold while dementia is projected to double every 20 years reaching ~115 million by 2050. AD is clinically characterized by progressive dementia and neuropathologically by neuronal and synapse loss, accumulation of amyloid plaques, and neurofibrillary tangles (NFTs) in specific brain regions. The preclinical or presymptomatic stage of AD-related brain changes may begin over 20 years before symptoms occur, making development of noninvasive biomarkers essential. Distinct from neuroimaging and cerebrospinal fluid biomarkers, plasma or serum biomarkers can be analyzed to assess (i) the presence/absence of AD, (ii) the risk of developing AD, (iii) the progression of AD, or (iv) AD response to treatment. No unifying theory fully explains the neurodegenerative brain lesions but neuroinflammation (a lethal stressor for healthy neurons) is universally present. Current consensus is that the earlier the diagnosis, the better the chance to develop treatments that influence disease progression. In this article we provide a detailed review and analysis of the role of the blood-brain barrier (BBB) and damage-associated molecular patterns (DAMPs) as well as coagulation molecules in the onset and progression of these neurodegenerative disorders.

MMP9-sensitive polymers mediate environmentally-responsive bivalirudin release and thrombin inhibition

MMP9-responsive bivalirudin-HPMA copolymers were synthesized for direct, local administration in rat spinal cord contusion injury models. Polymer-conjugated bivalirudin peptides maintained activity while demonstrating enzyme-mediated release upon MMP9 exposure and prolonged release from hyaluronic acid/methylcellulose (HAMC) hydrogels compared to free bivalirudin peptide. Localized administration of bivalirudin copolymers in vivo at the site of rat spinal cord injury decreased cellular proliferation and astrogliosis, suggesting the bivalirudin copolymer and HAMC hydrogel system are a promising therapeutic intervention for reducing immediate inflammatory responses and long term scarring.

Targeting the thrombin receptor modulates inflammation and astrogliosis to improve recovery after spinal cord injury

The deregulation of serine protease activity is a common feature of neurological injury, but little is known regarding their mechanisms of action or whether they can be targeted to facilitate repair. In this study we demonstrate that the thrombin receptor (Protease Activated Receptor 1, (PAR1)) serves as a critical translator of the spinal cord injury (SCI) proteolytic microenvironment into a cascade of pro-inflammatory events that contribute to astrogliosis and functional decline. PAR1 knockout mice displayed improved locomotor recovery after SCI and reduced signatures of inflammation and astrogliosis, including expression of glial fibrillary acidic protein (GFAP), vimentin, and STAT3 signaling. SCI-associated elevations in pro-inflammatory cytokines such as IL-1β and IL-6 were also reduced in PAR1-/- mice and co-ordinate improvements in tissue sparing and preservation of NeuN-positive ventral horn neurons, and PKCγ corticospinal axons, were observed. PAR1 and its agonist's thrombin and neurosin were expressed by perilesional astrocytes and each agonist increased the production of IL-6 and STAT3 signaling in primary astrocyte cultures in a PAR1-dependent manner. In turn, IL-6-stimulated astrocytes increased expression of PAR1, thrombin, and neurosin, pointing to a model in which PAR1 activation contributes to increased astrogliosis by feedforward- and feedback-signaling dynamics. Collectively, these findings identify the thrombin receptor as a key mediator of inflammation and astrogliosis in the aftermath of SCI that can be targeted to reduce neurodegeneration and improve neurobehavioral recovery.

Poly(lactic-co-glycolic) acid microspheres encapsulated in Pluronic F-127 prolong hirudin delivery and improve functional recovery from a demyelination lesion

Components of the blood have been proposed as potential therapeutic targets for improving cellular regeneration after injury and neurodegenerative disease. In this work, thrombin is shown to increase endogenous neural progenitor proliferation in the intact murine spinal cord. A local injection of heparin before a spinal cord injury reduces cell proliferation and astrogliogenesis associated with scarring. We sought to create depot-formulations of PLGA microsphere and Pluronic F-127 for sustained local delivery of two thrombin inhibitors, heparin and hirudin. Each hydrogel depot-formulation showed delayed drug release compared to microspheres or hydrogel alone. Animals with a lateral demyelination lesion showed a reduction in CD68+ macrophages when treated with hirudin-loaded PLGA/F-127 gels compared to control and heparin-treated animals. Moreover, hirudin-loaded materials showed an accelerated recovery in coordinated stepping and increased oligodendrocyte densities. Together, these data demonstrate that controlled delivery of hirudin accelerates functional recovery from a demyelination lesion in the spinal cord.

Kallikrein cascades in traumatic spinal cord injury: in vitro evidence for roles in axonopathy and neuron degeneration

Kallikreins (KLKs) are a family of 15 secreted serine proteases with emerging roles in neurologic diseases. To illuminate their contributions to the pathophysiology of spinal cord injury (SCI), we evaluated acute through chronic changes in the immunohistochemical appearance of 6 KLKs (KLK1, KLK5, KLK6, KLK7, KLK8, and KLK9) in postmortem human traumatic SCI cases, quantified their RNA expression levels in experimental murine SCI, and assessed the impact of recombinant forms of each enzyme toward murine cortical neurons in vitro. Temporally and spatially distinct changes in KLK expression were observed with partially overlapping patterns between human and murine SCI, including peak elevations (or reductions) during the acute and subacute periods. Kallikrein 9 showed the most marked changes and remained chronically elevated. Importantly, a subset of KLKs (KLK1, KLK5, KLK6, KLK7, and KLK9) were neurotoxic toward primary neurons in vitro. Kallikrein immunoreactivity was also observed in association with swollen axons and retraction bulbs in the human SCI cases examined. Together, these findings demonstrate that elevated levels of a significant subset of KLKs are positioned to contribute to neurodegenerative changes in cases of CNS trauma and disease and, therefore, represent new potential targets for the development of neuroprotective strategies.

Thrombomodulin is upregulated in cardiomyocytes during cardiac hypertrophy and prevents the progression of contractile dysfunction

BACKGROUND

Cardiac hypertrophy is a common response to pressure overload and leads to left ventricular (LV) dysfunction. Thrombomodulin (TM), an endothelial anticoagulant protein, was found to have direct effects on cellular proliferation and inflammation. We examined the TM expression in cardiomyocytes during cardiac hypertrophy and investigated its physiological significance.

METHODS AND RESULTS

TM expression was evaluated in cardiomyocytes from hearts of mice that underwent transverse aortic constriction (TAC). The effects of recombinant TM protein on cardiomyocytes apoptosis and related signaling pathways were examined. Recombinant TM protein was administered continuously in mice that underwent TAC, and serial LV function was determined. There was significant TM expression in cardiomyocytes during cardiac hypertrophy elicited by TAC in mice. TM treatment decreased doxorubicin-induced apoptosis of cardiomyocytes and increased the Bcl-2/Bax ratio. It also increased cardiomyocytes hypertrophy, expression of atrial natriuretic peptide, and significantly activated the extracellular signal-regulated kinase 1/2 (ERK1/2) and the phosphatidylinositol-3-kinase (PI3-K)/protein kinase B (Akt) signaling pathways in cardiomyocytes. Continuous TM supply after TAC prevented the progression of LV contractile dysfunction in mice.

CONCLUSIONS

TM treatment decreased cardiomyocyte apoptosis and maintained LV contractile function in response to pressure overload.

Thrombin-induced activation of astrocytes in mixed rat hippocampal cultures is inhibited by soluble thrombomodulin

Thrombin, a serine protease known for its role in coagulation, also induces a variety of protease activated receptor (PAR)-mediated responses in the central nervous system that contribute to many brain pathologies. Since the proteolytic specificity of thrombin is uniquely controlled by thrombomodulin (TM), we investigated the mechanisms by which thrombin and a recombinant soluble form of human TM (Solulin, INN: sothrombomodulin alpha; rhsTM) could influence rat hippocampal cultures. Treatment of hippocampal cultures with thrombin for up to 48h resulted in a significant morphological rearrangement with the formation of expansive cell-free areas (CFAs) and a reduction in cell viability; both effects were blocked by rhsTM. Treatment with the selective PAR-1 agonist, TRAP (SFLLRN) caused the formation of CFAs, suggesting that CFA formation involved PAR-1 signaling. Astrocytes prepared from PAR-1(-/-) mice also had an attenuated CFA response to thrombin. Thrombin-induced CFA formation was a consequence of cell movement and substantial changes in cell morphology, rather than due to cell detachment. Immunocytochemical and functional analyses revealed that the thrombin-sensitive cells within these hippocampal cultures were astrocytes. The effects of thrombin on CFA development were mediated by astrocyte-specific release of intracellular calcium and signalling through ERK1/2. rhsTM was able to attenuate thrombin-induced ERK1/2 phosphorylation. Finally, astrocytes were shown to maintain thrombin-sensitivity following neuronal depletion with NMDA, a result which was confirmed with pure astrocyte cultures. Hence thrombin mediates PAR-1-induced activation of hippocampal astrocytes, but not neurons, in a process that can be modulated by rhsTM.

Soluble thrombomodulin protects ischemic kidneys

Altered coagulation and inflammation contribute to the pathogenesis of ischemic renal injury. Thrombomodulin is a necessary factor in the anticoagulant protein C pathway and has inherent anti-inflammatory properties. We studied the effect of soluble thrombomodulin (sTM) in a hypoperfusion model of ischemic kidney injury. To markedly reduce infrarenal aortic blood flow and femoral arterial pressures, we clamped the suprarenal aorta of rats, occluding them 90%, for 60 min. Reversible acute kidney injury (AKI) occurred at 24 h in rats subjected to hypoperfusion. Histologic analysis at 24 h revealed acute tubular necrosis (ATN), and intravital two-photon microscopy showed flow abnormalities in the microvasculature and defects of endothelial permeability. Pretreatment with rat sTM markedly reduced both I-R-induced renal dysfunction and tubular histologic injury scores. sTM also significantly improved microvascular erythrocyte flow rates, reduced microvascular endothelial leukocyte rolling and attachment, and minimized endothelial permeability to infused fluorescence dextrans, assessed by intravital quantitative multiphoton microscopy. Furthermore, sTM administered 2 h after reperfusion protected against ischemia-induced renal dysfunction at 24 h and improved survival. By using an sTM variant, we also determined that the protective effects of sTM were independent of its ability to generate activated protein C. These data suggest that sTM may have therapeutic potential for ischemic AKI.

Neuroprotective effects of caspase-3 inhibition on functional recovery and tissue sparing after acute spinal cord injury

STUDY DESIGN

We used gene microarrays and found that caspase-related death genes were upregulated. We tested caspase inhibition and evaluated its effect on the spinal cord after traumatic injury.

OBJECTIVE

The logical extension of previous studies was to determine whether downstream CASP genes might also be involved and whether inhibition might prevent injury-induced cell death.

SUMMARY OF BACKGROUND DATA

Apoptotic cell death occurs in all endogenous cellular compartments of the spinal cord, peaking at 3 days after injury in neurons, astrocytes, and microglia. The downstream effector caspase-3 cleaves several important cellular sites after being activated by upstream initiator caspases. Along with others, we have previously identified caspase signature cleavage of PARP, alpha-fodrin, and DFF45/ICAD in the injured rat spinal cord. We also showed rapid upregulation of caspase-3 gene expression along with localization of active caspase-3 in neurons and activated microglia after SCI. Others have reported that a more general active-site mimetic peptide ketone, benzylocarbonyl-Val-Ala-Asp-fluromethylketone (zVAD-fmk) was neuroprotective after rat spinal cord injury (SCI).

METHODS

In this study, we administered the caspase-3 subfamily tetrapeptide cell permeable inhibitor Z-Asp(O-Me)-Glu(O-Me)-Val-Asp(O-Me) fluoromethyl ketone (DEVD-fmk) intraperitoneally 1 hour after laminectomy and moderate (25 g cm force) SCI in rats. RESULTS.: We used the open field locomotor rating (LRS) over a 14-day course and found statistically significant improvement in DEVD-fmk-treated rats, LRS, 9.8 +/- 0.93 SEM, compared with vehicle, 6.6 +/- 0.4 (P < 0.05). Histologic analysis of percent spinal cord tissue volume spared was 50% greater for DEVD-fmk versus control (P < 0.5).

CONCLUSION

These results indicate neuroprotection at both the cellular level and with substantial functional recovery, suggesting caspase-3 inhibition may be a viable therapy in the early hours after experimental SCI.

Activation profiles of human kallikrein-related peptidases by proteases of the thrombostasis axis

The human kallikrein-related peptidases (KLKs) comprise 15 members (KLK1-15) and are the single largest family of serine proteases. The KLKs are utilized, or proposed, as clinically important biomarkers and therapeutic targets of interest in cancer and neurodegenerative disease. All KLKs appear to be secreted as inactive pro-forms (pro-KLKs) that are activated extracellularly by specific proteolytic release of their N-terminal pro-peptide. This processing is a key step in the regulation of KLK function. Much recent work has been devoted to elucidating the potential for activation cascades between members of the KLK family, with physiologically relevant KLK regulatory cascades now described in skin desquamation and semen liquefaction. Despite this expanding knowledge of KLK regulation, details regarding the potential for functional intersection of KLKs with other regulatory proteases are essentially unknown. To elucidate such interaction potential, we have characterized the ability of proteases associated with thrombostasis to hydrolyze the pro-peptide sequences of the KLK family using a previously described pro-KLK fusion protein system. A subset of positive hydrolysis results were subsequently quantified with proteolytic assays using intact recombinant pro-KLK proteins. Pro-KLK6 and 14 can be activated by both plasmin and uPA, with plasmin being the best activator of pro-KLK6 identified to date. Pro-KLK11 and 12 can be activated by a broad-spectrum of thrombostasis proteases, with thrombin exhibiting a high degree of selectivity for pro-KLK12. The results show that proteases of the thrombostasis family can efficiently activate specific pro-KLKs, demonstrating the potential for important regulatory interactions between these two major protease families.

Investigation of the dose-dependent neuroprotective effects of agmatine in experimental spinal cord injury: a prospective randomized and placebo-control trial

OBJECT

No definitive treatment for spinal cord injuries (SCIs) exists, and more research is required. The use of agmatine [4-(aminobutyl)-guanidine-NH2-CH2-CH2-CH2-CH2-NH-C(-NH2)(=NH)], a guanidinium compound formed by decarboxylation of L-arginine by arginine decarboxylase, is a neurotransmitter-neuromodulator with both N-methyl-D-aspartate receptor (NMDAR)-antagonizing and nitric oxide synthase (NOS)-inhibiting activities. The purpose of this study was to demonstrate the dose-dependent activity of agmatine, an inducible NOS (iNOS) inhibitor and selective NMDAR antagonist, on biochemical and functional recovery in an experimental rat SCI model.

METHODS

This study involved 40 Wistar albino male rats. The rats were subjected to sleep-awake cycles for 7 days before surgery. In each group, general anesthesia was induced by a 60-mg/kg ketamine injection. For the surgical SCI model, a Yaşargil aneurysm clip was placed in the spinal cord. The study was conducted in the following four main groups: Group I (control group) laminectomy only; Group II, trauma-only group and SCI; Group III, laminectomy, SCI and agmatine 50 mg/kg for 10 days; and Group IV, laminectomy, SCI, and agmatine 100 mg/kg for 10 days. On Day 1, no statistical difference was observed in any group (p < 0.005, analysis of variance [ANOVA] and the Fisher protected least significant difference [PLSD]). On Day 2, no statistical difference was noted among Groups II, III, and IV (p = 0.27, p = 0.42, and p = 0.76, respectively; ANOVA and Fisher PLSD). Beginning on Day 3, recovery in Groups III and IV differed significantly from that in Group II (p < 0.005, ANOVA and Fisher PLSD), and a statistically significant difference between Groups III and IV was observed, which also was present on Days 5, 7, and 10 (p = 0.003, p = 0.0024, and p = 0.0036, respectively; ANOVA and Fisher PLSD). Several observations were noteworthy: motor function scores were reduced significantly in the spinal cord-injured rats compared with the controls (p < 0.005); on Day 1, the agreement of motor function scores in rats in each SCI group indicated that the traumatic event had been replicated equally across all groups (p = 0.59, p = 0.59, and p = 0.28); a statistically significant difference in motor function scores developed on Day 3 between the rats subjected to trauma alone (Group II) and those treated with agmatine (Groups III and IV) (p < 0.005); and no statistically significant intergroup difference in motor function existed at any postinjury interval between the 50- and 100-mg/kg/day agmatine-treated rats (p > 0.005).

CONCLUSIONS

Agmatine administration following SCI was shown to reduce NO levels significantly. No statistically significant intergroup difference in the reduction of NO levels was found between rats treated with 50- and 100-mg/kg/day doses of agmatine. Administration of a 100-mg/kg/day dose of agmatine reduced the NO levels to those measured in controls. The authors conclude that with additional studies into the role of agmatine, this drug may be helpful in the treatment of patients with SCIs.

Minocycline neuroprotects, reduces microgliosis, and inhibits caspase protease expression early after spinal cord injury

Minocycline, a clinically used tetracycline for over 40 years, crosses the blood-brain barrier and prevents caspase up-regulation. It reduces apoptosis in mouse models of Huntington's disease and familial amyotrophic lateral sclerosis (ALS) and is in clinical trial for sporadic ALS. Because apoptosis also occurs after brain and spinal cord (SCI) injury, its prevention may be useful in improving recovery. We analyzed minocycline's neuroprotective effects over 28 days following contusion SCI and found significant functional recovery compared to tetracycline. Histology, immunocytochemistry, and image analysis indicated statistically significant tissue sparing, reduced apoptosis and microgliosis, and less activated caspase-3 and substrate cleavage. Since our original report in abstract form, others have published both positive and negative effects of minocycline in various rodent models of SCI and with various routes of administration. We have since found decreased tumor necrosis factor-alpha, as well as caspase-3 mRNA expression, as possible mechanisms of action for minocycline's ameliorative action. These results support reports that modulating apoptosis, caspases, and microglia provide promising therapeutic targets for prevention and/or limiting the degree of functional loss after CNS trauma. Minocycline, and more potent chemically synthesized tetracyclines, may find a place in the therapeutic arsenal to promote recovery early after SCI in humans.