NAAG peptidase inhibitor reduces cellular damage in a model of TBI with secondary hypoxia

Dendrimer-enabled targeted delivery attenuates glutamate excitotoxicity and improves motor function in a rabbit model of cerebral palsy

Glutamate carboxypeptidase II (GCPII), localized on the surface of astrocytes and activated microglia, regulates extracellular glutamate concentration in the central nervous system (CNS). We have previously shown that GCPII is upregulated in activated microglia in the presence of inflammation. Inhibition of GCPII activity could reduce glutamate excitotoxicity, which may decrease inflammation and promote a 'normal' microglial phenotype. 2-(3-Mercaptopropyl) pentanedioic acid (2-MPPA) is the first GCPII inhibitor that underwent clinical trials. Unfortunately, immunological toxicities have hindered 2-MPPA clinical translation. Targeted delivery of 2-MPPA specifically to activated microglia and astrocytes that over-express GCPII has the potential to mitigate glutamate excitotoxicity and attenuate neuroinflammation. In this study, we demonstrate that 2-MPPA when conjugated to generation-4, hydroxyl-terminated polyamidoamine (PAMAM) dendrimers (D-2MPPA) localize specifically in activated microglia and astrocytes only in newborn rabbits with cerebral palsy (CP), not in controls. D-2MPPA treatment led to higher 2-MPPA levels in the injured brain regions compared to 2-MPPA treatment, and the extent of D-2MPPA uptake correlated with the injury severity. D-2MPPA was more efficacious than 2-MPPA in decreasing extracellular glutamate level in ex vivo brain slices of CP kits, and in increasing transforming growth factor beta 1 (TGF-β1) level in primary mixed glial cell cultures. A single systemic intravenous dose of D-2MPPA on postnatal day 1 (PND1) decreased microglial activation and resulted in a change in microglial morphology to a more ramified form along with amelioration of motor deficits by PND5. These results indicate that targeted dendrimer-based delivery specifically to activated microglia and astrocytes can improve the efficacy of 2-MPPA by attenuating glutamate excitotoxicity and microglial activation.

Novel image analysis tool for rapid screening of cell morphology in preclinical animal models of disease

The field of cell biology has seen major advances in both cellular imaging modalities and the development of automated image analysis platforms that increase rigor, reproducibility, and throughput for large imaging data sets. However, there remains a need for tools that provide accurate morphometric analysis of single cells with complex, dynamic cytoarchitecture in a high-throughput and unbiased manner. We developed a fully automated image-analysis algorithm to rapidly detect and quantify changes in cellular morphology using microglia cells, an innate immune cell within the central nervous system, as representative of cells that exhibit dynamic and complex cytoarchitectural changes. We used two preclinical animal models that exhibit robust changes in microglia morphology: (1) a rat model of acute organophosphate intoxication, which was used to generate fluorescently labeled images for algorithm development; and (2) a rat model of traumatic brain injury, which was used to validate the algorithm using cells labeled using chromogenic detection methods. All ex vivo brain sections were immunolabeled for IBA-1 using fluorescence or diaminobenzidine (DAB) labeling, images were acquired using a high content imaging system and analyzed using a custom-built algorithm. The exploratory data set revealed eight statistically significant and quantitative morphometric parameters that distinguished between phenotypically distinct groups of microglia. Manual validation of single-cell morphology was strongly correlated with the automated analysis and was further supported by a comparison with traditional stereology methods. Existing image analysis pipelines rely on high-resolution images of individual cells, which limits sample size and is subject to selection bias. However, our fully automated method integrates quantification of morphology and fluorescent/chromogenic signals in images from multiple brain regions acquired using high-content imaging. In summary, our free, customizable image analysis tool provides a high-throughput, unbiased method for accurately detecting and quantifying morphological changes in cells with complex morphologies.

Exosomes derived from bone marrow mesenchymal stem cells attenuate neurological damage in traumatic brain injury by alleviating glutamate-mediated excitotoxicity

BACKGROUND

Traumatic brain injury (TBI) is one of the major contributors to disability and death worldwide. Glutamate-mediated excitotoxicity, one of the secondary injuries occurring after TBI, leads to extreme neuronal apoptosis, and can be a potential target for intervention. Bone marrow mesenchymal stem cells-derived exosomes (BMSCs-Exos) have demonstrated neuroprotective effects on TBI. However, their precise role and the underlying mechanism by which they regulate glutamate-mediated excitotoxicity have not yet been determined. Therefore, this study aimed to determine whether BMSCs-Exos alleviate glutamate excitotoxicity post-TBI and their associated mechanism.

METHODS

BMSCs-Exos were extracted from the BMSCs incubation medium and identified by transmission electron microscopy, nanoparticle trafficking analysis, and western blotting. The neuroprotective effects of BMSCs-Exos on glutamate excitotoxicity were investigated in the glutamate-mediated excitotoxicity neuronal cell model and the TBI rat model (TBI induced by controlled cortical impact) using western blotting and TUNEL assay. Cortical lesion samples were collected post-TBI on day-1 and day-14 to study histology. In addition, cortical lesion volume on days 1, 3 and 7 following TBI was determined using T2-weighted magnetic resonance imaging (MRI), and cognitive function was assessed at 4 weeks following TBI using the Morris water maze (MWM) test.

RESULTS

BMSC-Exos were observed to be spherical with a mean diameter of 109.9 nm, and expressed exosomal markers CD9, CD81 and TSg101. BMSCs-Exos were efficiently endocytosed by astrocytes after co-incubation for 24 h. In vitro studies revealed that 125 μM of glutamate significantly induced neuronal apoptosis, which was attenuated by BMSCs-Exos in astrocyte-neuron co-cultures. This attenuation was mediated by the upregulation of glutamate transporter-1 (GLT-1) level and the downregulation of p-p38 MAPK level in astrocytes. Similar results were obtained in vivo, wherein we verified that PKH67-labeled BMSCs-Exos administered intravenously could reach the perilesional cortex crossing the blood-brain barrier and significantly reduce glutamate levels in the perilesional cortex of the TBI rat, accompanied by increased GLT-1 level and downregulation in p-p38 MAPK level. Additionally, western blotting and TUNEL staining also revealed that BMSCs-Exos significantly downregulated the expression of pro-apoptosis markers, including cleaved caspase-3 and cleaved caspase-9, and attenuated neuronal apoptosis following TBI. Immunohistochemical analysis and Nissl staining showed that BMSCs-Exos significantly increased GLT-1-positive cells, and the number of apoptotic neurons decreased in the perilesional cortex. Moreover, MRI and MWM results revealed that BMSCs-Exos significantly minimized cortical lesion volume and ameliorated cognitive function after TBI. The underlying neuroprotective mechanism of BMSCs-Exos may be due to an increase in GLT-1 level in astrocytes by blocking the p38 MAPK signaling pathway.

CONCLUSION

Taken together, our findings demonstrate that the implementation of BMSCs-Exos may be an effective prospective therapy for attenuating post-TBI neurological damage.

N-Acetyl-Aspartyl-Glutamate in Brain Health and Disease

N-acetyl-aspartyl-glutamate (NAAG) is the most abundant dipeptide in the brain, where it acts as a neuromodulator of glutamatergic synapses by activating presynaptic metabotropic glutamate receptor 3 (mGluR3). Recent data suggest that NAAG is selectively localized to postsynaptic dendrites in glutamatergic synapses and that it works as a retrograde neurotransmitter. NAAG is released in response to glutamate and provides the postsynaptic neuron with a feedback mechanisms to inhibit excessive glutamate signaling. A key regulator of synaptically available NAAG is rapid degradation by the extracellular enzyme glutamate carboxypeptidase II (GCPII). Increasing endogenous NAAG—for instance by inhibiting GCPII—is a promising treatment option for many brain disorders where glutamatergic excitotoxicity plays a role. The main effect of NAAG occurs through increased mGluR3 activation and thereby reduced glutamate release. In the present review, we summarize the transmitter role of NAAG and discuss the involvement of NAAG in normal brain physiology. We further present the suggested roles of NAAG in various neurological and psychiatric diseases and discuss the therapeutic potential of strategies aiming to enhance NAAG levels.

Genetic Modulators of Traumatic Brain Injury in Animal Models and the Impact of Sex-Dependent Effects

Traumatic brain injury (TBI) is a major health problem causing disability and death worldwide. There is no effective treatment, due in part to the complexity of the injury pathology and factors affecting its outcome. The extent of brain injury depends on the type of insult, age, sex, lifestyle, genetic risk factors, socioeconomic status, other co-injuries, and underlying health problems. This review discusses the genes that have been directly tested in TBI models, and whether their effects are known to be sex-dependent. Sex differences can affect the incidence, symptom onset, pathology, and clinical outcomes following injury. Adult males are more susceptible at the acute phase and females show greater injury in the chronic phase. TBI is not restricted to a single sex; despite variations in the degree of symptom onset and severity, it is important to consider both female and male animals in TBI pre-clinical research studies.

Acute damage to the blood–brain barrier and perineuronal net integrity in a clinically-relevant rat model of traumatic brain injury

Closed-head, frontal impacts in which the brain undergoes both lateral and rotational acceleration comprise the majority of human traumatic brain injury (TBI). Here, we utilize a clinically relevant model to examine the effects of a single concussion on aspects of brain integrity: the blood-brain barrier, the perineuronal nets (PNNs), and diffuse axonal injury. Adult, male Sprague-Dawley rats received either a frontal, closed-head concussive TBI, or no injury and were evaluated at 1- or 7-day post-injury. Using immunolabeling for albumin, we observed a significant increase in the permeability of the blood-brain barrier at 1-, but not 7-day post-injury. Breakdown of the PNN, as measured by the binding of wisteria floribunda, was observed at 1-day post-injury in the dorsal, lateral, and ventral cortices. This difference was resolved at 7-day. Finally, axonal injury was identified at both 1- and 7-day post-injury. This preclinical model of closed-head, frontal TBI presents a useful tool with which to understand better the acute pathophysiology of a single, frontal TBI.

Separate N-acetyl aspartyl glutamate, N-acetyl aspartate, aspartate, and glutamate quantification after pediatric mild traumatic brain injury in the acute phase

PURPOSE

To separately measure N-acetyl aspartul glutamate (NAAG), N-acetyl aspartate (NAA), aspartate (Asp), and glutamate (Glu) concentrations in white matter (WM) using J-editing techniques in patients with mild traumatic brain injury (mTBI) in the acute phase.

METHODS

Twenty-four patients with closed concussive head injury and 29 healthy volunteers were enrolled in the current study. For extended ¹ H MRS examination, patients and controls were equally divided into two subgroups. In subgroup 1 (12 patients/15 controls), NAAG and NAA concentrations were measured in WM separately with MEGA-PRESS (echo time/repetition time [TE/TR] = 140/2000 ms; δ ON NAA / δ OFF NAA = 4.84/4.38 ppm, δ ON NAAG / δ OFF NAAG = 4.61/4.15 ppm). In subgroup 2 (12 patients/14 controls), Asp and Glu concentrations were acquired with MEGA-PRESS (TE/TR = 90/2000 ms; δ ON Asp / δ OFF Asp = 3.89/5.21 ppm) and TE-averaged PRESS (TE from 35 ms to 185 ms with 2.5-ms increments; TR = 2000 ms) pulse sequences, respectively.

RESULTS

tNAA and NAAG concentrations were found to be reduced, while NAA concentrations were unchanged, after mild mTBI. Reduced Asp and elevated myo-inositol (mI) concentrations were also found.

CONCLUSION

The main finding of the study is that the tNAA signal reduction in WM after mTBI is associated with a decrease in the NAAG concentration rather than a decrease in the NAA concentration, as was thought previously. This finding highlights the importance of separating these signals, at least for WM studies, to avoid misinterpretation of the results. NAAG plays an important role in selectively activating mGluR3 receptors, thus providing neuroprotective and neuroreparative functions immediately after mTBI. NAAG shows potential for the development of new therapeutic strategies for patients with injuries of varying severity.

N-acetylaspartylglutamate (NAAG) and glutamate carboxypeptidase II: An abundant peptide neurotransmitter-enzyme system with multiple clinical applications

N-Acetylaspartylglutamate (NAAG) is the third most prevalent neurotransmitter in the mammalian nervous system, yet its therapeutic potential is only now being fully recognized. Drugs that inhibit the inactivation of NAAG by glutamate carboxypeptidase II (GCPII) increase its extracellular concentration and its activation of its receptor, mGluR3. These drugs warrant attention, as they are effective in animal models of several clinical disorders including stroke, traumatic brain injury and schizophrenia. In inflammatory and neuropathic pain studies, GCPII inhibitors moderated both the primary and secondary pain responses when given systemically, locally or in brain regions associated with the pain perception pathway. The finding that GCPII inhibition also moderated the motor and cognitive effects of ethanol intoxication led to the discovery of their procognitive efficacy in long-term memory tests in control mice and in short-term memory in a mouse model of Alzheimer's disease. NAAG and GCPII inhibitors respectively reduce cocaine self-administration and the rewarding effects of a synthetic stimulant. Most recently, GCPII inhibition also has been reported to be efficacious in a model of inflammatory bowel disease. GCPII was first discovered as a protein expressed by and released from metastatic prostate cells where it is known as prostate specific membrane antigen (PSMA). GCPII inhibitors with high affinity for this protein have been developed as prostate imaging and radiochemical therapies for prostate cancer. Taken together, these data militate in favor of the development and application of GCPII inhibitors in more advanced preclinical research as a prelude to clinical trials.

Enhanced Oral Bioavailability of 2-(Phosphonomethyl)-pentanedioic Acid (2-PMPA) from its (5-Methyl-2-oxo-1,3-dioxol-4-yl)methyl (ODOL)-Based Prodrugs

2-(Phosphonomethyl)-pentanedioic acid (2-PMPA) is a potent (IC₅₀ = 300 pM) and selective inhibitor of glutamate carboxypeptidase II (GCPII) with efficacy in multiple neurological and psychiatric disease preclinical models and more recently in models of inflammatory bowel disease (IBD) and cancer. 2-PMPA (1), however, has not been clinically developed due to its poor oral bioavailability (<1%) imparted by its four acidic functionalities (c Log P = -1.14). In an attempt to improve the oral bioavailability of 2-PMPA, we explored a prodrug approach using (5-methyl-2-oxo-1,3-dioxol-4-yl)methyl (ODOL), an FDA-approved promoiety, and systematically masked two (2), three (3), or all four (4) of its acidic groups. The prodrugs were evaluated for in vitro stability and in vivo pharmacokinetics in mice and dog. Prodrugs 2, 3, and 4 were found to be moderately stable at pH 7.4 in phosphate-buffered saline (57, 63, and 54% remaining at 1 h, respectively), but rapidly hydrolyzed in plasma and liver microsomes, across species. In vivo, in a single time-point screening study in mice, 10 mg/kg 2-PMPA equivalent doses of 2, 3, and 4 delivered significantly higher 2-PMPA plasma concentrations (3.65 ± 0.37, 3.56 ± 0.46, and 17.3 ± 5.03 nmol/mL, respectively) versus 2-PMPA (0.25 ± 0.02 nmol/mL). Given that prodrug 4 delivered the highest 2-PMPA levels, we next evaluated it in an extended time-course pharmacokinetic study in mice. 4 demonstrated an 80-fold enhancement in exposure versus oral 2-PMPA (AUC_0-t: 52.1 ± 5.9 versus 0.65 ± 0.13 h*nmol/mL) with a calculated absolute oral bioavailability of 50%. In mouse brain, 4 showed similar exposures to that achieved with the IV route (1.2 ± 0.2 versus 1.6 ± 0.2 h*nmol/g). Further, in dogs, relative to orally administered 2-PMPA, 4 delivered a 44-fold enhanced 2-PMPA plasma exposure (AUC_0-t for 4: 62.6 h*nmol/mL versus AUC_0-t for 2-PMPA: 1.44 h*nmol/mL). These results suggest that ODOL promoieties can serve as a promising strategy for enhancing the oral bioavailability of multiply charged compounds, such as 2-PMPA, and enable its clinical translation.

Mitochondrial uncoupling prodrug improves tissue sparing, cognitive outcome, and mitochondrial bioenergetics after traumatic brain injury in male mice

Traumatic brain injury (TBI) results in cognitive impairment, which can be long-lasting after moderate to severe TBI. Currently, there are no FDA-approved therapeutics to treat the devastating consequences of TBI and improve recovery. This study utilizes a prodrug of 2,4-dinitrophenol, MP201, a mitochondrial uncoupler with extended elimination time, that was administered after TBI to target mitochondrial dysfunction, a hallmark of TBI. Using a model of cortical impact in male C57/BL6 mice, MP201 (80 mg/kg) was provided via oral gavage 2-hr post-injury and daily afterwards. At 25-hr post-injury, mice were euthanized and the acute rescue of mitochondrial bioenergetics was assessed demonstrating a significant improvement in both the ipsilateral cortex and ipsilateral hippocampus after treatment with MP201. Additionally, oxidative markers, 4-hydroxyneneal and protein carbonyls, were reduced compared to vehicle animals after MP201 administration. At 2-weeks post-injury, mice treated with MP201 post-injury (80 mg/kg; q.d.) displayed significantly increased cortical sparing (p = .0059; 38% lesion spared) and improved cognitive outcome (p = .0133) compared to vehicle-treated mice. Additionally, vehicle-treated mice had significantly lower (p = .0019) CA3 neuron count compared to sham while MP201-treated mice were not significantly different from sham levels. These results suggest that acute mitochondrial dysfunction can be targeted to impart neuroprotection from reactive oxygen species, but chronic administration may have an added benefit in recovery. This study highlights the potential for safe, effective therapy by MP201 to alleviate negative outcomes of TBI.

Enhanced Brain Delivery of 2-(Phosphonomethyl)pentanedioic Acid Following Intranasal Administration of Its γ-Substituted Ester Prodrugs

2-(Phosphonomethyl)pentanedioic acid (2-PMPA) is a potent and selective inhibitor of glutamate carboxypeptidase-II (GCPII) with efficacy in multiple neurological and psychiatric disease models, but its clinical utility is hampered by low brain penetration due to the inclusion of multiple acidic functionalities. We recently reported an improvement in the brain-to-plasma ratio of 2-PMPA after intranasal (IN) dosing in both rodents and primates. Herein, we describe the synthesis of several 2-PMPA prodrugs with further improved brain delivery of 2-PMPA after IN administration by masking of the γ-carboxylate. When compared to IN 2-PMPA in rats at 1 h post dose, γ-(4-acetoxybenzyl)-2-PMPA (compound 1) resulted in significantly higher 2-PMPA delivery to both plasma (4.1-fold) and brain (11-fold). Subsequent time-dependent evaluation of 1 also showed high brain as well as plasma 2-PMPA exposures with brain-to-plasma ratios of 2.2, 0.48, and 0.26 for olfactory bulb, cortex, and cerebellum, respectively, as well as an improved sciatic nerve to plasma ratio of 0.84. In contrast, IV administration of compound 1 resulted in similar plasma exposure of 2-PMPA versus the IN route (AUC_IV: 76 ± 9 h·nmol/mL versus AUC_IN: 99 ± 24 h·nmol/mL); but significantly lower nerve and brain tissue exposures with tissue-to-plasma ratios of 0.21, 0.03, 0.04, and 0.04 in nerve, olfactory bulb, cortex, and cerebellum, respectively. In primates, IN administration of 1 more than doubled 2-PMPA concentrations in the cerebrospinal fluid relative to previously reported levels following IN 2-PMPA. The results of these experiments provide a promising strategy for testing GCPII inhibition in neurological and psychiatric disorders.

Role of glutamate receptors and glial cells in the pathophysiology of treatment-resistant depression

Treatment-resistant depression (TRD) causes substantial socioeconomic burden. Although a consensus on the definition of TRD has not yet been reached, it is certain that classic monoaminergic antidepressants are ineffective for TRD. One decade ago, many researchers found ketamine, an N-methyl-d-aspartate receptor (NMDAR) antagonist, to be an alternative to classic monoaminergic antidepressants. The major mechanisms of action of ketamine rapidly induce synaptogenesis in the brain-derived neurotrophic factor (BDNF) pathway. Although excessive glutamatergic neurotransmission and consequent excitotoxicity were considered a major cause of TRD, recent evidence suggests that the extrasynaptic glutamatergic receptor signal pathway mainly contributes to the detrimental effects of TRD. Glial cells such as microglia and astrocytes, early life adversity, and glucocorticoid receptor dysfunction participate in complex cross-talk. An appropriate reuptake of glutamate at the astrocyte is crucial for preventing 'spill-over' of synaptic glutamate and binding to the extrasynaptic NMDA receptor. Excessive microglial activation and the inflammatory process cause astrocyte glutamatergic dysfunction, which in turn activates microglial function. Early life adversity and glucocorticoid receptor dysfunction result in vulnerability to stress in adulthood. A maladaptive response to stress leads to increased glutamatergic release and pro-inflammatory cytokines, which then activate microglia. However, since the role of inflammatory mediators such as pro-inflammatory cytokines is not specific for depression, more disease-specific mechanisms should be identified. Last, although much research has focused on ketamine as an alternative antidepressant for TRD, its long-lasting effectiveness and adverse events have not been rigorously demonstrated. Additionally, evidence suggests that substantial brain abnormalities develop in ketamine abusers. Thus, more investigations for ketamine and other novel glutamatergic agents are needed.

Combined Treatment of an Amyotrophic Lateral Sclerosis Rat Model with Recombinant GOT1 and Oxaloacetic Acid: A Novel Neuroprotective Treatment

BACKGROUND/AIM

The sporadic form of the disease affects the majority of amyotrophic lateral sclerosis (ALS) patients. The role of glutamate (Glu) excitotoxicity in ALS has been extensively documented and remains one of the prominent hypotheses of ALS pathogenesis. In light of this evidence, the availability of a method to remove excess Glu from brain and spinal cord extracellular fluids without the need to deliver drugs across the blood-brain barrier and with minimal or no adverse effects may provide a major therapeutic asset, which is the primary aim of this study.

METHODS

The therapeutic efficacy of the combined treatment with recombinant Glu-oxaloacetate-transaminase (rGOT) and its co-factor oxaloacetic acid (OxAc) has been tested in an animal model of sporadic ALS.

RESULTS

We found that OxAc/rGOT treatment provides significant neuroprotection to spinal cord motor neurons. It also slows down the development of motor weakness and prolongs survival.

CONCLUSION

In this study we bring evidence that the administration of Glu scavengers to rats with sporadic ALS inhibited the massive death of spinal cord motor neurons, slowed the onset of motor weakness and prolonged survival. This treatment may be of high clinical significance for the future treatment of chronic neurodegenerative diseases.

Existence of glia mitigated ketamine-induced neurotoxicity in neuron-glia mixed cultures of neonatal rat cortex and the glia-mediated protective effect of 2-PMPA

The present study compared ketamine-induced neurotoxicity in the neuron-glia mixed cultures and neuronal cultures and further explored the neuroprotective effect of the NAAG peptidase inhibitor 2-(phosphonomethyl) pentanedioic acid (2-PMPA). Firstly, Rosenfeld's staining and immunofluorescence staining of microtubule-associated protein 2 (MAP2) and glial fibrillary acidic protein (GFAP) were used to address the difference of morphology in the mixed cultures and neuronal cultures. Our results showed that neurons and astrocytes grew in good conditions. The ratio of neurons and astrocytes in the mixed cultures was around 1:1, and the purity of neurons in the neuronal cultures is 91.3%. Furthermore, ketamine was used to test the hypothesis that the presence of a higher proportion of glia in the mixed cultures would be protective against ketamine-induced neurotoxicity in the mixed cultures compared with neuronal cultures. The results showed that ketamine-induced morphological changes, cell viability decrease and lactate dehydrogenase (LDH) levels increase were significantly mitigated in neuron-glia mixed cultures compared with neuronal cultures. Furthermore, 2-PMPA was included to further explore efficient protective drug for ketamine-induced neurotoxicity. Our results showed that 2-PMPA reduced ketamine-induced decrease of cell viability and increase of LDH levels in the mixed cultures but not in the neuronal cultures. Further morphological changes of neurons and astrocytes also indicated that 2-PMPA could improve ketamine damaged neurons in the mixed cultures instead of neuronal cultures. These results indicate that glia protect neurons from ketamine-induced neurotoxicity. These data further suggest that glia mediate the neuroprotective effect of 2-PMPA and 2-PMPA has the potential to treat ketamine-induced neurotoxicity in vivo. Delineating the mechanisms underlying the communication between neurons and glia and the neuroprotective effects of 2-PMPA in the mixed cultures to ketamine-induced neurotoxicity require further investigation.

Structural characterization of P1'-diversified urea-based inhibitors of glutamate carboxypeptidase II

Urea-based inhibitors of human glutamate carboxypeptidase II (GCPII) have advanced into clinical trials for imaging metastatic prostate cancer. In parallel efforts, agents with increased lipophilicity have been designed and evaluated for targeting GCPII residing within the neuraxis. Here we report the structural and computational characterization of six complexes between GCPII and P1'-diversified urea-based inhibitors that have the C-terminal glutamate replaced by more hydrophobic moieties. The X-ray structures are complemented by quantum mechanics calculations that provide a quantitative insight into the GCPII/inhibitor interactions. These data can be used for the rational design of novel glutamate-free GCPII inhibitors with tailored physicochemical properties.

Traumatic brain injury using mouse models

The use of mouse models in traumatic brain injury (TBI) has several advantages compared to other animal models including low cost of breeding, easy maintenance, and innovative technology to create genetically modified strains. Studies using knockout and transgenic mice demonstrating functional gain or loss of molecules provide insight into basic mechanisms of TBI. Mouse models provide powerful tools to screen for putative therapeutic targets in TBI. This article reviews currently available mouse models that replicate several clinical features of TBI such as closed head injuries (CHI), penetrating head injuries, and a combination of both. CHI may be caused by direct trauma creating cerebral concussion or contusion. Sudden acceleration-deceleration injuries of the head without direct trauma may also cause intracranial injury by the transmission of shock waves to the brain. Recapitulation of temporary cavities that are induced by high-velocity penetrating objects in the mouse brain are difficult to produce, but slow brain penetration injuries in mice are reviewed. Synergistic damaging effects on the brain following systemic complications are also described. Advantages and disadvantages of CHI mouse models induced by weight drop, fluid percussion, and controlled cortical impact injuries are compared. Differences in the anatomy, biomechanics, and behavioral evaluations between mice and humans are discussed. Although the use of mouse models for TBI research is promising, further development of these techniques is warranted.

The prostate-specific membrane antigen: lessons and current clinical implications from 20 years of research

OBJECTIVE

Despite a multitude of detection and treatment advances in the past 2 decades, prostate cancer remains the second leading cause of deaths due to cancer among men in the United States. Technological evolution and expanding knowledge of tumor biomarkers have invigorated exploration in prostate cancer therapeutics. Prostate-specific membrane antigen (PSMA) was one of the first prostate cancer biomarkers successfully cloned. Since then, it has been characterized as the prototypical cell-surface marker for prostate cancer and has been the subject of intense clinical inquiry. In this article, we review the relevant research in PSMA on the 20th anniversary of its cloning.

METHODS AND MATERIALS

A PubMed search using the keywords "prostate-specific membrane antigen" or "glutamate carboxypeptidase II" provided 1019 results. An additional 3 abstracts were included from scientific meetings. Articles were vetted by title and abstract with emphasis placed on those with clinically relevant findings.

RESULTS

Sixty articles were selected for inclusion. PSMA was discovered and cloned in 1993. Its structure and function were further delineated in the ensuing decade. Consensus sites of expression in normal physiology are prostate, kidney, nervous system, and small intestine. PSMA has been implicated in the neovasculature of several tumors including urothelial and renal cell carcinomas. In prostate cancer, expression of PSMA is directly related to the Gleason grade. PSMA has been tested both in imaging and therapeutics in a number of prostate cancer clinical trials. Several recent approaches to target PSMA include the use of small molecule inhibitors, PSMA-based immunotherapy, RNA aptamer conjugates, and PSMA-targeted prodrug therapy. Future study of PSMA in prostate cancer might focus on its intracellular functions and possible role in tumor neurogenesis.

CONCLUSIONS

Twenty years from its discovery, PSMA represents a viable biomarker and treatment target in prostate cancer. Research to delineate its precise role in prostate carcinogenesis and within the therapeutic armamentarium for patients with prostate cancer remains encouraging.

HIF-1α involves in neuronal apoptosis after traumatic brain injury in adult rats

Hypoxia-inducible factor-1α (HIF-1α), a well-identified hypoxia-related protein, is involved in regulating the biological functions of various cell types including neurons. The traditional biological function of HIF-1α is promoting the transcription of some pro-survival genes when exposing to low oxygen conditions. Meanwhile, some studies also point out that HIF-1α shows the detrimental role in several central nervous system (CNS) disorders. Up to now, the knowledge of HIF-1α function in CNS is still limited. To investigate whether HIF-1α is involved in CNS impairment and repair, we employed a traumatic brain injury model in adult rats. Upregulation of HIF-1α was observed in the injured brain cortex by western blot analysis and immunohistochemistry staining. Terminal deoxynucleotidyl transferase deoxy-UTP nick-end labeling (TUNEL) and 4',6-diamidino-2-phenylindole (DAPI) staining suggested that HIF-1α was relevant to neuronal apoptosis after brain injury. In addition, glutamate excitotoxic model of primary cortex neurons was introduced to further investigate the role of HIF-1α in neuronal apoptosis; the result implied HIF-1α was associated with the regulation of p53 and BNIP3 in the apoptotic neurons. Based on our data, we suggested that HIF-1α might play an important role in neuronal apoptosis after traumatic brain injury in rat, which might also provide a basis for the further study on its role in regulating the transcription of target genes in apoptotic neurons, and might gain a novel strategy for the clinical therapy for traumatic brain injury.

NAAG peptidase inhibitor improves motor function and reduces cognitive dysfunction in a model of TBI with secondary hypoxia

Immediately following traumatic brain injury (TBI) and TBI with hypoxia, there is a rapid and pathophysiological increase in extracellular glutamate, subsequent neuronal damage and ultimately diminished motor and cognitive function. N-acetyl-aspartyl glutamate (NAAG), a prevalent neuropeptide in the CNS, is co-released with glutamate, binds to the presynaptic group II metabotropic glutamate receptor subtype 3 (mGluR3) and suppresses glutamate release. However, the catalytic enzyme glutamate carboxypeptidase II (GCP II) rapidly hydrolyzes NAAG into NAA and glutamate. Inhibition of the GCP II enzyme with NAAG peptidase inhibitors reduces the concentration of glutamate both by increasing the duration of NAAG activity on mGluR3 and by reducing degradation into NAA and glutamate resulting in reduced cell death in models of TBI and TBI with hypoxia. In the following study, rats were administered the NAAG peptidase inhibitor PGI-02776 (10mg/kg) 30 min following TBI combined with a hypoxic second insult. Over the two weeks following injury, PGI-02776-treated rats had significantly improved motor function as measured by increased duration on the rota-rod and a trend toward improved performance on the beam walk. Furthermore, two weeks post-injury, PGI-02776-treated animals had a significant decrease in latency to find the target platform in the Morris water maze as compared to vehicle-treated animals. These findings demonstrate that the application of NAAG peptidase inhibitors can reduce the deleterious motor and cognitive effects of TBI combined with a second hypoxic insult in the weeks following injury.